Chapter 4: The Salmonids of Bristol Bay 41 Chapter 4 [T]he net result of losing [Bristol Bay sockeye] The Salmonids of Bristol Bay population and life history diversity could be a tenfold increase in the frequency of fishery clo- In 2010, over 40 million wild sockeye salmon sures, generating considerable hardship for people returned from the ocean to spawn in the Bristol Bay who rely on consistent annual returns for their basin. The 28.5 million sockeye harvested commercially livelihoods . in the bay that year produced an ex-vessel value of just —“Population Diversity and the Portfolio Effect in an under $150 million (ADFG 2011a), a figure that does Exploited Species” (Schindler et al. 2010) not include the retail, recreational, or cultural value of the harvest (discussed in chapter 7). Over 11 million sockeye escaped the nets to spawn in 2010 (ADFG Bristol Bay salmon returns is 2.2 times lower than it 2011a), ensuring the continued viability of the largest would be if the system consisted of a single population, sustainable harvest of wild salmon on the planet. rather than the several hundred discrete populations it currently consists of.” Population and life history 4.1 Habitat and Adaptation diversity reduce variability in production at the basin or stock scale (Bristol Bay has 15 discrete stocks) because Salmon require several different types of freshwater the impacts of disturbance or unfavorable environmen- habitat to successfully complete their lifecycles, includ- tal conditions can be minimized. For example, juvenile ing areas suitable for spawning, incubation, rearing, sockeye exhibit a variety of strategies when migrating and migration (Meehan 1991). The unique richness and to or returning from the ocean. Some spend one year diversity of Bristol Bay’s salmon populations are driven rearing in freshwater while others spend two; similarly, by the region’s extraordinary abundance of varied, sockeye may remain in the ocean for one to three years near-pristine, hydrologically well-connected, and pro- before returning to spawn as adults. This complex age ductive freshwater habitats. The region’s habitat com- structure within a population increases the likelihood plexity, coupled with salmon’s strong natal homing that temporally or spatially limited disturbances (i.e., tendencies, creates distinct, locally adapted populations environmental changes that do not impact the entire with a high degree of adaptive specialization to individ- basin or persist over many years) do not impact all of ual stream conditions (Hilborn et al. 2003 , Ramstad et the individuals in a particular cohort. al. 2009). This dampening effect on the impact of disturbance The Kvichak River provides a good example of is critical in maintaining the productivity of the entire habitat-driven genetic adaptation for sockeye. At least system and allowing sustainable commercial, recre- 150 sockeye populations have been identified in the ational, and subsistence harvests year after year. In Kvichak watershed, 38 of which reside in Lake Clark fact, Schindler et al. (2010) found that if Bristol Bay and the upper Newhalen River (Demory et al. 1964, produced just a single homogeneous population, the Young and Woody 2007). It is possible that as many resulting increased variability in run size would “lead as 200 to 300 discrete spawning aggregates occupy the to ten times more frequent fisheries closures.” In addi- Kvichak system alone (Habicht et al. 2004, Ramstad et tion to the bounty enjoyed by humans, the benefits of al. 2004, Ramstad et al. 2009). Local genetic adapta- sustained salmon runs are shared among numerous tions include size and age at maturity, which depends other species (discussed in section 4.2). to a large degree on stream size, and timing of spawn- Although Bristol Bay’s population diversity and ing (Hilborn et al. 2003, Woody 2004, Ramstad et al. population-level habitat specialization ensures that 2009). Habicht et al. (2007) found that 97.2% of the salmon can take advantage of a wide range of habi- genetic diversity of Bristol Bay sockeye salmon could tats and limits the impacts of environmental distur- be explained by differentiating among the spawning bance, it leaves them vulnerable to larger scale habitat sites where they were collected. alterations. For example, to sustain genetically adapted This habitat-dependent population diversity limits local populations, water quality characteristics must the fluctuations in salmon runs commonly seen in remain within a narrow range, and small changes, systems with less complex and available habitats. In a such as increases in dissolved copper concentrations, recently published paper, Schindler et al. (2010) use 50 can be lethal or highly disruptive to survival (Eisler years of Bristol Bay sockeye population data to high- 2000, Baldwin et al. 2003, Sandahl et al. 2006, Hecht light the role that life history and population diversity et al. 2007, Sandahl et al. 2007, Tierney et al. 2010). play in sustaining a steady yield of a heavily exploited Once genetic diversity is lost from salmon popula- species. The research finds that “variability in annual tions through habitat destruction or degradation, the 42 Table 2. Fish Species in Bristol Bay Drainages. All salmon spawn in fresh water. Anadromous fish (indicated by “ANA” in the table) spawn in fresh waters and migrate to marine waters to feed. Resident, non-anadromous fish (“NON”) spawn and feed entirely in fresh water, often with substantial seasonal movements between habitats within a given drainage (Quinn 2004). These are known as potamodromous (POT). In amphidromous (AMP) populations, juveniles move from salt water to the lower rivers to feed. In some Bristol Bay species (including salmon), essentially all individuals have anadromous life histories. In others, all individuals have nonanadromous life histories (lake trout, arctic grayling, and pygmy and round whitefish). And in yet other species, individual fish may exhibit either anadromous or nonanadromous life histories (rainbow trout/steelhead, Dolly Varden, Bering cisco, least cisco, humpback whitefish). Salmon are “semelparous”, mean- ing they reproduce only once per lifetime and then die. Other Bristol Bay salmonids are “iteroparous” and can spawn multiple times during a lifetime (Morrow 1980, Stearns 1992, Mecklenburg et al. 2002, ADFG 2008b, Brown et al. 2009). Family Name Common Name Scientific Name Principal Life History Petromyzontidae/lampreys arctic lamprey Lethenteron camtschaticum ANA Petromyzontidae Alaskan brook lamprey Lethenteron alaskense NON Petromyzontidae Pacific lamprey Entosphenus tridentatus ANA Clupeidae/herrings Pacific herring Clupea pallasii AMP Catostomidae/suckers longnose sucker Catostomus catostomus NON Esocidae/pikes northern pike Esox lucius NON Umbridae/mudminnows Alaska blackfish Dallia pectoralis NON Chum salmon (photo by Paul Vecsei). Osmeridae/smelts rainbow smelt Osmerus mordax ANA Osmeridae pond smelt Hypomesus olidus NON Osmeridae eulachon Thaleichthys pacificus ANA Salmonidae/salmonids Bering cisco Coregonus laurettae ANA and NON Salmonidae humpback whitefish Coregonus pidschian ANA and NON Salmonidae least cisco Coregonus sardinella ANA and NON Coho salmon (photo by Barrie Kovish). Salmonidae pygmy whitefish Prosopium coulteri NON Salmonidae round whitefish Prosopium cylindraceum NON Salmonidae coho salmon Oncorhynchus kisutch ANA Salmonidae Chinook salmon Oncorhynchus tshawytscha ANA Salmonidae sockeye salmon Oncorhynchus nerka ANA Salmonidae chum salmon Oncorhynchus keta ANA Salmonidae pink salmon Oncorhynchus gorbuscha ANA Sockeye salmon (photo by Barrie Kovish). Salmonidae rainbow trout Oncorhynchus mykiss POT and ANA Salmonidae arctic char Salvelinus alpinus POT Salmonidae Dolly Varden Salvelinus malma ANA and POT Salmonidae lake trout Salvelinus namaycush NON Salmonidae arctic grayling Thymallus arcticus POT Gadidae/cods burbot Lota lota POT Gadidae Pacific cod Gadus macrocephalus AMP Gadidae saffron cod Eleginus gracilis AMP Dolly Varden (photo by Wild Salmon Center). Gasterosteidae/sticklebacks threespine stickleback Gasterosteus aculeatus NON and ANA Gasterosteidae ninespine stickleback Pungitius pungitius NON Cottidae/sculpins coastrange sculpin Cottus aleuticus NON Cottidae slimy sculpin Cottus cognatus NON Cottidae Pacific staghorn sculpin Leptocottus armatus AMP Pleuronectidae/ flounders arctic flounder Pleuronectes glacialis AMP Rainbow trout (photo by Wild Salmon Center). Pleuronectidae starry flounder Platichthys stellatus AMP Chapter 4: The Salmonids of Bristol Bay 43 likelihood of the species surviving over the long term is diminished (Rich 1939, Nehlsen et al. 1991, Spence et al. 1996, Hilborn et al. 2003, Schindler et al. 2010). This fact has been demonstrated repeatedly. Salmon populations prospered in cold waters throughout large regions of North America for thousands of years, but over the last century they have been extirpated from substantial portions of their ranges as a result of human changes to their habitats (Nehlsen et al. 1991). Decades of resource extraction, construction of migration barri- ers, hatchery production, and harvest have caused the decline and extinction of many populations (Nehlsen et al. 1991, Frissell 1993, Huntington et al. 1996). If a major disturbance, such as a flood, volcano, freeze, disease, or tailings dam failure eliminates all Bristol Bay’s resident salmonids and ocean-going species, such as this salmon from a system, populations in other watersheds coho, are genetically adapted to live within