This paper was written as part of the 2011 Alaska Oceans Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.

Potential Impacts of Pacific Salmon (Oncorhynchus spp.) Hatcheries on Pacific Herring (Clupea pallasii) in Lynn Canal

Authors

Tyler Houseweart
Seth Brickey
Elise Christey
Sam Kurland
Martina Miller

Team Absolute Vorticity

Juneau-Douglas High School
10014 Crazy Horse Drive
Juneau, AK 99801-8529

Abstract

The Lynn Canal Pacific herring (Clupea pallasii) population declined rapidly between 1971 and 1981, for reasons not completely understood. The population has not rebounded, and the Lynn Canal herring fishery has remained closed since 1982. It is unusual for herring populations to remain depressed for this length of time in the absence of a fishery. This suggests the presence of factors that are preventing the resurgence of the herring population. A number of possible factors have been hypothesized, including disease, increased predation by marine mammals, anthropogenic noise pollution, marine pollution, and habitat degradation. We discuss each of these hypotheses in turn, and suggest the presence of an additional factor. We hypothesize that a factor acting to keep the Lynn Canal herring population depressed is predation by, and competition with, Pacific salmon (Oncorhynchus spp.) released from the Douglas Island Pink and Chum Macaulay salmon hatchery. We discuss the Lynn Canal ecosystem and the role of herring within it; herring are key component of the Lynn Canal food web. Therefore, it would be beneficial to the ecosystem if the population were to rebound. To that end, we establish a management plan. We present relevant background information pertaining to management, including information on herring fisheries, salmon fisheries, and the Douglas Island Pink and Chum hatchery. We propose that research be conducted to identify reasons why the population remains depressed, including the extent to which salmon compete with and prey upon Lynn Canal herring. We also recommend the establishment of a task force to discuss research findings and provide recommendations to the Alaska Department of Fish and Game and the Alaska Board of Fisheries. The goal of our recommendations is to facilitate a recovery of the Lynn Canal herring population and develop an ecosystem-based, multispecies approach to the management of the Lynn Canal.

Introduction

Pacific herring (Clupea pallasii) is an integral species to the marine ecosystems and fishing industry of Southeast Alaska (SEAK). Although a commercial herring fishery does not currently exist in Lynn Canal (LC), herring remain a key component in a food web that supports commercial and sport fisheries in the area. Herring are also a large component of the diets of many marine mammals. These marine mammals draw tourists from around the world, bringing in millions of dollars of revenue to SEAK.

Humans have impacted herring populations directly and indirectly via the development of herring fisheries, and the effects of marine pollution, as well as spawning habitat degradation. The LC herring population declined rapidly between 1971 and 1981, and has not rebounded since. This suggests the presence of ongoing factors that are preventing the resurgence of the herring population, as it is unusual for herring populations to take so long to rebound in the absence of a fishery (Hebert, pers. comm.).

As a result of the depressed population status, the Sierra Club requested that the LC herring population be listed as an endangered species in 2007. Their request included an analysis of potential factors suppressing the population. Hypothesized factors included degradation of habitat, disease, and increased predation by large marine mammals (Rorick, 2007).

The Sierra Club did not address a potentially important factor in its initial analysis and petition request: the interspecific competition with juvenile Pacific salmon (Oncorhynchus spp.) and predation by adult salmon. The effect of this competition and predation could be exacerbated by the recent rise of commercial salmon hatcheries (Van Alen, pers. comm.). Later, in a letter to the National Marine Fisheries Service (NMFS), Rorick (2008) suggests that hatchery-raised salmon are negatively impacting herring.

In this paper we define the LC ecosystem, outline human impacts thereupon and propose a management strategy to address the depressed population of LC herring. In particular, we discuss the role that hatchery-reared salmon may have in suppressing a recovery of the LC herring population and outline an alternative approach to the management of the LC ecosystem. We also discuss the implications our management plan has for the species involved as well as the community of Juneau.

Lynn Canal Ecosystem

Lynn Canal (Figure 1) is a marine fjord that extends from 59.30°N to 54.40°N, and 130°W to 137°W (Martin and Williams, 1924), is approximately 145 kilometers (km) long (Rorick, 2007), and divides into the Chilkat and Chilkoot Inlets at its head (Martin, 1924). Berners Bay and Auke Bay are located on the eastern side of LC (Carlson, 1984). The shoreline is a rocky primary coast resulting from glacial erosional processes (Martin and Williams, 1924). LC is less saline than the outside waters of SEAK due to a large freshwater influx from glacial melt, precipitation, and its distance from the more saline waters of the open ocean (Heintz, pers. comm.; Wing et al. 2006). Summer surface temperatures reach approximately 5°C to 6°C (Rorick, 2007) above those of winter; this seasonal surface thermocline results from greater insolation and reduced winds during the spring and summer months (Carlson, 1984). Tidal ranges in LC are greater than those of the outside waters of SEAK due to the great distance between LC and the nearest amphidromic point, and the tidal resonance inherent to enclosed bodies of water (Garrison, 2005).

Rich supplies of terrestrial nutrients and sediments, mixed into the water column by winter storms, support large plankton blooms that typically cloud surface visibility by April or early May (Carlson, 1984). These blooms are a major food source for many prey species (NMFS, 2005). The migrations and spawning periods of many species, such as herring, are timed to coincide with the plankton bloom (Carlson, 1984).

Herring occupy an intermediary trophic level and are an integral part of the diets of many consumers. They are preyed upon by salmon (Groot and Margolis, 1991), seabirds (Monagle, pers. comm.), humpback whales (Megaptera novaeangliae), and Steller sea lions (Eumetopias jubatus) (Heintz, pers. comm.; Womble and Sigler, 2006). SEAK historically supported sufficient wild salmon biomass for the establishment of salmon fisheries. To support growing demand and prevent collapse of natural stocks, however, augmentation via salmon hatcheries became popular; in LC, the Douglas Island Pink and Chum (DIPAC) salmon hatchery began operation in 1976 (http://dipac.net/corp.htm).

Human activity has altered the LC ecosystem. Construction of houses and marine terminals has degraded the habitat utilized by a wide variety of organisms (Rorick, 2007). The ongoing operation of the Kensington mine near Berners Bay is of great concern, as the operation of any large-scale industrial endeavor will inevitably result in some degree of pollution and habitat degradation (Rorick, pers.comm.). Additionally, increased marine traffic, both personal and commercial, likely causes harm to the LC ecosystem through incidental pollution inherent to the operation of marine vessels (Hood, pers. comm.).

Salmon and Herring Biology

The biology of salmon is well known and well described in Groot and Margolis (1991). There are five species of Alaskan Pacific Salmon that are commercially harvested; chinook (O. tshawytscha), sockeye (O. nerka), coho (O. kisutch), chum (O. keta) and pink (O. gorbuscha).

In southeastern waters, sand lance (Ammodytes hexapterus), herring, walleye pollock (Theragra chalcogramma), and capelin (Mallotus villosus) are important components of the juvenile sockeye salmon diet. Analysis of adult sockeye salmon diet at 82 locations in the northern Pacific Ocean and the Bering Sea showed amphipods as the dominant prey with 43%, followed by fish (18%); squid (16%); euphuasids (12%); copepods (7%); pteropods (2%); and other organisms (2%) (Favorite, 1970). Chum eat euphausids, hyperiid amphipods, small fish, pteropods, copepods, squid, and squid larvae. Chinook salmon prey upon small fish, particularly herring, as well as pelagic amphipods and crab megalopa. Pink salmon diet at sea consists primarily of euphausids, amphipods, small fish and squid. Herring, sand lance, and unidentified fish remains account for 34.6% of coho diet. Amphipods account for 26.7%, and crab megalops 26.2% (Groot and Margolis, 1991). The diets of herring and salmon overlap considerably (Table 1).

Herring spawn in the spring along shorelines in shallow sub-tidal and inter-tidal zones where eggs adhere to kelp, eelgrass (Zostera marina), and any other structure that is available to them (Rorick, 2007). Though the degree of spawning fidelity is poorly understood, herring in SEAK spawn in similar areas year after year, indicating that these areas are important to preserve (Carls et al. 2008). Many organisms, marine and otherwise, rely on the herring eggs for food.

Distribution and survival of herring larvae, which hatch after three to four weeks, depend heavily on local currents. Larvae require currents to deposit them in areas where there is low predation and high zooplankton productivity for an optimal development. As larvae, herring feed on copepods, invertebrate eggs, and diatoms (Mitchell, 2006). They grow for two to three months, after which time they are considered juveniles. As juveniles, they remain in large schools close to shore for their first summer and feed primarily on invertebrates such as harpaticoid and calanoid copepods, decapod larvae, gammarid amphipods, barnacle larvae, and chaetognaths.

Adult herring feed near the surface on copepods, euphausiids, amphipods and small fishes at night, and move into deeper waters during the day (Mitchell, 2006). Adult herring of LC feed primarily on copepods and euphausiids during the summer and generally cease feeding entirely in the winter, and draw instead from stored energy reserves (Vollenweider, pers. comm.).

Herring are a major food source for many predators including Steller sea lions, humpback whales and all salmon species. Herring comprise 53% of the diet of humpback whales in LC during the winter (Moran, 2007) and are found in 90% of the scats of sea lions in LC (Vollenweider, pers. comm.). The Eastern Distinct Population Segment of the Steller sea lion is listed as "Threatened" by the Endangered Species Act (ESA) and as "Depleted" by the Marine Mammal Protection Act (MMPA). The Central North Pacific humpback whale is listed as "Endangered" under the ESA and "Depleted" under the MMPA.

In its review of the Sierra Club's petition to list the LC population segment of Pacific herring, the National Oceanic and Atmospheric Administration (NOAA) declined to define the LC segment as a biologically distinct population. This judgment was made according to genetic parameters (Van Alen, pers. comm., Kurland, pers. comm.), which may be excessively narrow in scope. Many scientists have concluded that LC herring are in fact behaviorally distinct, if not genetically so (Hood, pers. comm.) and we see merit in the argument presented by Rorick (2007), who discusses at great length a number of justifications for defining the segment as a biologically distinct population. Thus, we refer to LC herring as a "population" throughout this document.

Lynn Canal Herring Fishery Collapse

Between 1971 and 1981, the LC population of herring declined rapidly (Figure 2). Although the cause is uncertain, it has been suggested that this decline was due to a period of overfishing. In 1982, under pressure from the fishing industry, the Governor of Alaska (Bill Sheffield) overrode the Alaska Department of Fish and Game (ADF&G) emergency closure of the LC herring sac roe fishery (Rauwolf et al., 2007), placing political concerns over biological considerations (Thornton et al., 2010).

After the 1982 harvest, the LC herring fishery was closed to further commercial harvests. Since then, the herring population has remained depressed (Thynes et al., 2010). The extent of herring spawn in LC used to be approximately 48.3 km however, since the crash, they have only been utilizing 4.83 km of spawning habitat (Rorick, 2007). In fact, since 1983, the spawning herring biomass has remained an average of 3,709 metric tons (mt) below the harvest threshold of 4,536 mt set by ADF&G. This problem is even more noteworthy when one considers the suggestion by Rauwolf et al. (2007) that the harvest threshold set by ADF&G is too low, which they assert is because the spawning biomass was already substantially lower than historic levels by the time population monitoring began.

Possible Factors Affecting Lynn Canal Herring: Human Impacts

The LC ecosystem has been altered by human activity. It has been suggested that these alterations have contributed to the depression of the LC herring population. Rorick (2007) hypothesizes that degradation of critical herring spawning grounds, such as the construction of the Juneau ferry terminal in Auk Nu Cove, has had noteworthy negative effects on the LC herring population. Indeed, Rorick states, "Historic overfishing depleted the population initially, but the destruction and degradation of spawning grounds are the primary reason [sic] for the herring's failure to recover." This explanation is not universally accepted; some scientists in the Juneau community consider it to be a primary or secondary factor, while others think it plays much less of a role. Other areas with similar habitat degradation have healthy herring populations (Hebert, pers. comm.). Additionally, herring repeatedly spawn in the same areas year after year for unknown reasons and as a result they are not utilizing all of the available spawning habitat in LC (Monagle, pers. comm.). Therefore it is likely that habitat degradation plays at most a secondary role, influencing the population in conjunction with other, more important factors.

Rorick (2007) postulates that increased anthropogenic noise pollution in and around LC has negatively impacted herring by interfering with sounds that the species use to communicate. While increased noise pollution may be an important factor influencing the LC herring population, other populations in SEAK are subject to similar levels of anthropogenic noise yet have populations that are not depressed, suggesting that this is not a leading factor.

Possible Factors Affecting Lynn Canal Herring: Natural Factors

Rorick (2007) briefly discusses the possibility that increased predation by large marine mammals, such as Steller sea lions and humpback whales, has impacted the LC herring population. However, he discounts the influence of these predators, suggesting that predation pressure by the currently ESA-listed mammals is probably less now than it was before these predators were depleted (Rorick, 2007). Humpback whale populations have been rebounding in recent years at a rate of about 7% per year (Heintz, pers. comm.), but have not recovered to anywhere near the high levels that existed before commercial whaling in the Pacific (Hood, pers. comm.). Estimates of herring consumption by humpback whales in the winter are low relative to the total number of herring: whales only consume approximately 2% of the available herring biomass (Heintz et al., 2010). We acknowledge that whales may have an increasing impact on the herring population, but we think there are other major contributing factors. Regardless, there are currently no regulatory measures that can be applied to regulate the predation of herring by whales in LC, so any management plans should focus mainly on the regulation of other factors.

Rorick also discusses the possibility of disease as a factor capable of suppressing a recovery of the herring population. Pearson et al. (1999) hypothesize that disease was a major factor in the Prince William Sound herring collapse, but state that its influence cannot be definitively established. Pearson et al. (1999) also state that disease generally has little impact on a herring population unless another factor is present that weakens the population initially. While it is true that the LC population is weakened, disease is relatively low in the LC herring population (Vollenweider, pers. comm.), and we would expect a disease potent enough to severely impair the herring population in LC to be more prominent.

Salmon Hypothesis

We hypothesize that the augmentation of wild populations of salmon by the Douglas Island Pink and Chum hatchery is a possible contributing factor preventing a herring population rebound in LC. In 2009, the DIPAC Macaulay Hatchery released a total of 110,432,857 salmon, including 108,989,466 chum, 559,429 coho, and 883,962 chinook (Figure 2). Juvenile salmon compete with herring for food, such as copepods and euphausiids. Later in life, some species of salmon prey upon herring, Figure 2 illustrates the potential relationship between herring and hatchery released salmon. In a classic predator-prey relationship, if the prey were to undergo a severe decline, the population of the predator would also undergo a decline, maintaining equilibrium. In the case of salmon and herring in LC however, this does not occur for three reasons. First, salmon are capable of switching prey sources (Heintz, pers. comm.), minimizing their reliance on herring as a prey source. Second, a decrease in herring would also decrease competition between the species, increasing the number of salmon. Third, and most importantly, salmon populations are being augmented by hatcheries; they compose a majority of the salmon catch in the Juneau area (McDowell Group, 2009). Thus, salmon in LC have the potential to act not only as predator or competitor of the herring, but also potentially as a long-term suppressor. Consultation with local scientists has indicated that our hypothesis is plausible (Hood, pers. comm., Van Alen, pers. comm., Hebert, pers. comm., Monagle, pers. comm., Heintz, pers. comm.).

When juvenile salmon move out of their respective streams during early spring, they occupy estuaries that often contain eelgrass beds (Groot and Margolis, 1991), a habitat in which herring eggs are commonly laid (Lassuy, 1989). Juvenile salmon and herring (all stages), consume zooplankton, especially copepods and euphausiids. Adult salmon also consume some zooplankton targeted by herring. Copepods and euphausiids comprise 7% and 12% of sockeye salmon diet respectively, and the diet of juvenile chum salmon consists primarily of copepods (Groot and Margolis, 1991). Euphausiids comprise 60% of chum diet in May-June, while euphausiids and copepods are also listed as primary food sources for juvenile pink salmon (Groot and Margolis, 1991). Purcell (2001) indicates that herring and pink salmon have a Percent Similarity Index value of 34.2. Calaniod copepods and euphausiids are of particular importance with euphausiids comprising 27% of the adult pink salmon diet (Groot and Margolis, 1991). Though DIPAC ceased releasing pink salmon in spring of 2002, during the 24 years prior, they could have potentially had a role in suppressing the herring population.

Salmon prey on herring in two ways; juveniles eat larvae during their estuarine life in the late spring, and as adults, salmon eat herring (Table 1). Chinook consume the most herring, comprising 60-68% of their diet in SEAK. Dietary analysis of chinook and chum salmon feeding in the open ocean indicated that fish comprise the majority of their diet (Groot and Margolis, 1991) and of the DIPAC species released, coho and chinook salmon likely compete with and prey upon herring the most (Wing, pers. comm.).

The 1993 Prince William Sound (PWS) herring crash is widely considered to have been caused by the 1989 Exxon Valdez oil spill; this view is not unanimous. Indeed, Pearson et al. (1999) state, "the low level of oil exposure documented for herring in 1989 and the following years…indicate[s] that the 1989 oil spill did not contribute to the 1993 decline." It is important to note that the PWS herring decline occurred shortly after salmon enhancement programs in PWS were expanded and it is possible that the herring crash resulted from this, not oil pollution. This suggests the possibility that hatcheries have contributed to the similar herring suppression in LC. The PWS case differs from the LC case in that we propose that salmon released from hatcheries are a factor suppressing a recovery of the herring population, whereas in PWS, it is possible that hatchery releases may have actually caused the initial decline, in addition to suppressing their numbers afterwards.

The Sitka Sound herring population is flourishing in regards to biomass, and is supporting the largest herring fishery in SEAK (Monagle, pers. comm.). Though there is a large salmon hatchery located nearby, the Medvejie Hatchery, this does not necessarily mean that the herring in Sitka Sound are being impacted in the same way as those in LC. The ecosystems differ and there are undoubtedly numerous other factors at work that could affect the interactions between salmon and herring in Sitka Sound.

Management Considerations: Herring Economics

Herring are of great value to the coastal communities bordering their populations. The first commercial herring fishery in Alaska began operation in 1878 (Northern Economics Inc., 2009). In the sac-roe fishery, herring are harvested in nets just before spawning and transported to shore, where their eggs are collected (ADF&G, 2009). Japanese herring stocks declined in the 1960's, forcing Japan to obtain herring from overseas. Currently, almost all of the roe ends up in the Japanese marketplace as a salted product that sells for over $220/kg (ADF&G, 2009). Coastal communities use herring eggs collected from kelp and hemlock boughs for subsistence purposes (ADF&G, 2009). There is also a commercial fishery for roe-on-kelp in SEAK, which was opened in 1968 (Rauwolf, 2006). There are two main methods of collection employed by this fishery. First, divers collect naturally spawned eggs from the kelp by hand and with rakes. Second, herring are also caught in nets and transported to impoundments containing kelp. These eggs are then collected from the kelp.

The Alaskan herring bait fishery began in the early 1900's (ADF&G, 2009). It is the smallest of the herring fisheries by catch (ADF&G, 2009), but it has remained the most consistent, fluctuating between 1,800 and 2,700 mt per year (Northern Economics Inc., 2009). The demand for herring bait increased in the 1970's with the development of crab fisheries (Northern Economics Inc., 2009) with catches increasing for several years afterward (ADF&G, 2009).

Herring catch in Alaska was 28,746 mt in 2007, comprising approximately 90% of the U.S. Pacific Ocean herring harvest. Herring harvesting accounted for 4% of the total harvesting jobs in Alaska, or approximately 1,109 jobs, in 2006. In 2007, approximately $5,430,000 was paid to herring harvesters. Recently, the Alaska sac roe harvest has averaged about 45,500 mt, but the herring roe market has been in decline due to lower overseas consumption rates (Northern Economics Inc., 2009).

Management Considerations: Salmon Fishery

Salmon provide 29% of the first wholesale value of the Alaska seafood industry, and 22% of the ex-vessel value of Alaska seafood industry. The salmon industry employs 55% of Alaska's seafood harvesting workforce (Northern Economics Inc., 2009). Salmon were first harvested commercially in 1878 in Sitka and Klawock. In 1915-1924, an average of 41 million salmon per year was caught in SEAK alone. The salmon began to "crash" when the annual harvest dropped from 31 million salmon in 1945-1949 to 19 million salmon in 1950-1954 (Colt, 2007). With changing management and the help of hatcheries, the harvest of salmon increased from 16,329.33 mt in 1975 to 70,715.05 mt in 1983 (Sisk, 2005).

Salmon also provide economic benefits for SEAK through tourism and sport fishing. In fact, sportfish day charters alone brought $7,440,000 to the SEAK economy in 2006 (Colt, 2007). Salmon is also an important subsistence food. In 2003, the subsistence and personal catch of salmon was 79,434 salmon (ADF&G, 2005).

Management Considerations: Hatchery Economics

The Alaska State Legislature first authorized ADF&G to issue permits to private-nonprofit (PNP) salmon hatcheries in 1974. The goal of these salmon hatcheries was to augment the Alaska salmon stocks and increase the productivity of local fisheries (http://dipac.net/corp.htm). "During the 1990s, the Alaska Program produced 27-54 million adult salmon annually, which accounted for 14-37% of the annual common-property salmon harvest. It is second in size and productivity to the Japanese ocean-ranching program," (Bert, 2007). DIPAC is one of three PNP aquaculture associations in SEAK along with the Northern Southeast Aquaculture Association stationed in Sitka and the Southern Southeast Aquaculture Association in Ketchikan. DIPAC was opened under such a permit in 1976 (Figure 2), as a small-scale hatchery. DIPAC currently operates the Macaulay Salmon Hatchery, located in Juneau, and the Snettisham Hatchery, located 64.37 km south of Juneau (McDowell Group, 2009). The Macaulay Salmon hatchery currently conducts remote releases in several locations, including Gastineau Channel, Amalga Boat Harbor, Limestone, Fish Creek, Auke Bay, Skagway, and Twin Lakes (http://dipac.net/2009_hatchery_releases.htm).

In 2008, commercial gillnetters harvested $9.6 million of DIPAC salmon, of which Alaska resident fishermen harvested 90%. Approximately 44% of these earnings went to residents of Juneau (McDowell, 2009). In addition to the economic benefits gained from catch, the citizens of SEAK gain jobs and revenue from the salmon processing industry. The McDowell Group (2009) determined that in 2008, the direct and indirect economic gains induced by DIPAC salmon totaled approximately $5.9 million, of which approximately $3.6 million was labor income for fishermen and other workers.

Management Considerations: Socioeconomic and Political Concerns

DIPAC and the industries it supports provide jobs and support the local economy. In addition, DIPAC is a central component of the Juneau community. Over 100,000 tourists visit the DIPAC Macaulay Hatchery each summer. The hatchery also hosts over 3,000 local children annually for an educational program about marine environments (McDowell Group, 2009). This hatchery is utilized, both directly and indirectly, by subsistence fishermen, tourists, fishermen, processors, school children, and many other members of the community.

Management Plan

Herring play a crucial role in the LC food web, and their restoration to historical levels would be beneficial to the ecosystem as a whole and could potentially support commercial and subsistence fisheries. Therefore, the objective of this management plan is to: 1) first establish a research plan to more conclusively determine why the LC herring population remains depressed including studies designed to address the salmon hypothesis; and 2) provide an adaptive management approach to modify conditions in LC in order to test facilitate a recovery of the herring population.

Statistically meaningful data is required for sound decision making. Previously, LC herring biomass estimates were conducted with minimal time and resources, and as a result, ADF&G views estimates of the historical biomass as uncertain (Hebert, pers. comm.). Fortunately, ADF&G has recently switched from using hydroacoustic imaging techniques as the primary method of estimating herring biomass (Hebert, pers. comm.) to the more accurate method of dive surveys (Monagle, pers. comm.). We encourage ADF&G to continue to employ this technique, while using hydroacoustic imaging as a supplemental approach during months when herring are not spawning.

Research and analysis must be conducted to elucidate the cause of the LC herring suppression. It is possible that hatchery-released salmon are contributing to this suppression. We propose that research should be designed to test whether it is occurring. An important first step of this research would be to perform a comprehensive analysis of the relationship between the herring population and hatchery-released salmon in all areas where they interact. This would include an analysis of how size-classes, age-classes, and population sizes of herring are affected by the presence and magnitude of hatchery salmon releases; essentially, studies should be conducted to determine the extent to which hatchery-released salmon are preying upon and competing with herring. Investigations should include stomach analysis of both herring and salmon juveniles and adults in LC, as well as thorough assessments of zooplankton in sites without rearing herring or salmon, a test release site, and a site from which salmon are being released currently.

We propose that intensive zooplankton assay research be initiated and conducted in areas where herring are currently spawning (e.g. vicinity of Berners Bay), where salmon are being released (Figure 1), and in an area removed from current hatchery release sites and herring spawning grounds (such as Howard Bay, located in the junction between southern LC and northern Chatham Strait). This research, to be conducted for 3-5 years to account for yearly fluctuations, would establish baseline levels of zooplankton. Following the baseline research, remote release sites in Amalga Harbor and Auke Bay would be moved from their current locations near the herring spawning grounds to the test ecosystem; zooplankton in all areas would continue to be monitored. The results of this study could be used to establish the effect of hatchery releases on zooplankton that herring also prey upon. Zooplankton are an important food source for many species, and are integral to a healthy ecosystem. Information on the effects of hatcheries on zooplankton, therefore, is vital for a truly multi-species and ecosystem-based approach. Any effect, or lack thereof, that altering the salmon release site location had in the herring population could also be observed. An alternative approach to determine the effect of hatchery released salmon on the herring population would be to follow the technique used in a study conducted by NOAA (Heintz et al., in press), Humpback Whale (Megaptera novaeangliae) Predation and the Case for Top-Down Control of Local Herring (Clupea pallasii) Populations In the Gulf of Alaska.

If the salmon hypothesis was supported by the research plan above (e.g. an increase in herring population size occurred in Berners Bay in the absence of hatchery salmon), we would recommend that a discussion regarding the decision-making process used to determine how hatchery releases are made take place. Currently, the management plan for hatcheries is primarily driven by economics. The parameters that are used when determining the amount of release are stimulation of the local economy and the ability of the hatchery to remain financially solvent (Monagle, pers. comm.). We think these parameters should be expanded to include the ecological effects of releases. Some currently feel there is sufficient and compelling evidence regarding the effect of salmon on herring to merit a closure of all salmon hatcheries in SEAK at this time. However, we recognize that even if our hypothesis was accepted after research, such closures would not be politically feasible. It is necessary to incorporate political and social concerns while formulating a solution.

It is important that research towards other factors not be abandoned; additional research efforts to monitor LC herring should be initiated or continued. In particular, biomass, mixing with other herring populations, the occurrence of diseases, the effects of human impacts, and predation by large marine mammals should be monitored.

A task force should be established to discuss research findings and management options, and provide recommendations to authority organizations such as ADF&G. This task force would include scientists from ADF&G, NOAA, and independent agencies, representatives from DIPAC, salmon fishermen, and other involved community members. This community involvement would result in recommendations that reflect not only the concerns of scientists, but also those whose livelihood depends on the successful management of the LC ecosystem.

There have been many other novel thoughts on how to encourage resurgence in the herring population. One idea is the establishment of a herring hatchery but this might only increase competition for food resources. Another idea is the transportation of a portion of the herring population to another potential spawning ground. Novel approaches such as these should be considered by the task force, as they could be potentially valuable to the successful management of the LC ecosystem.

Conclusion

The Pacific herring population in LC has remained in a depressed state for almost 30 years. We hypothesize that augmentation of Pacific salmon is a primary suppressing factor. The current depressed state of the LC herring population weakens the overall health of the LC ecosystem. Therefore, it is important to establish why the population continues to be depressed; we recommend an investigatory approach similar to the one contained in our management plan. We recognize that ours is not the only approach to addressing this problem, but our recommendations contain elements that are likely to be essential for the success of any management solution: careful scientific research, consideration of adaptive measures based on the results, consideration of the interactions between species, and active involvement of key stakeholders. Regardless of the approach chosen, action must be taken, as the alternative—continued degradation of the Lynn Canal ecosystem—is unacceptable.

Figures and Tables

herring spawning areas

Figure 1. Shows the locations of historic and recent herring spawn areas and DIPAC release sites in Lynn Canal. The area of herring spawn was severely reduced between 1972-1979 and 1996-2003. Letters A-E represent these release sites. In 2010, Boat Harbor (A) and Amalga (B) released chum; Auke Bay (C) and Fish Creek (D) released chinook; and Gastineau Channel (E) released chum, coho and chinook.
Source: (http://dipac.net/2009_hatchery_releases.htm) (McDowell Group, 2009) (Rorick, 2007)

graph of salmon releases and herring spawning biomass in Lynn Canal

Figure 2.Illustrates the total salmon releases from DIPAC salmon hatchery and herring biomass in Lynn Canal. The decline of herring biomass corresponds to the increase in salmon hatchery releases, suggesting interaction between the species.
Source: http://dipac.net/

graph of salmon releases and herring spawning biomass in Lynn Canal

Table 1. Shows diet overlap of herring and salmon in their juvenile (J) and adult (A) life stages. All salmon diet information came from Groot and Margolis (1991). Herring dietary information obtained from Rorick (2007) and Mitchell (2006).

References