< Ecosystem Status Report

Gulf of Alaska - Ecological Trends

Executive summary

Full Report - Last updated 2018

  • In the Alaskan Shelf region sampled by the continuous plankton recorder, diatom abundance anomalies were very high in 2017 relative to those in the previous 6 years (p. 65).
  • Copepod community size anomalies were larger for the Alaskan Shelf and oceanic habitats in 2017, after a period of smaller size copepods during the marine heat wave (2013–2016), and mesozooplankton biomass anomalies were positive for the 4th consecutive year (p. 65).
  • In 2018, mean biomass (mg/m3 ) of calanoids and euphausiids along the Seward Line during May were higher than the long-term mean (1998–2017) This was the 4th consecutive year for above average calanoid biomass (p. 66).
  • In 2017, lower than average abundances of zooplankton were observed in Prince William Sound, while more warm water copepods were seen earlier in the year followed by a mixture of warm and cold water species (p. 67).
  • Zooplankton density in Icy Strait in 2018 was above average and the 5th highest density observed over the 22-year time series. Zooplankton density was below average from 2013–2016 (p. 71).
  • In 2018, the density of small calanoids was above average, the 5th highest density in the 22-year time series. All other taxa were at (gastropods) or below (large calanoid copepods, euphausiids, and hyperiid amphipods) average (p. 71).
  • The lipid content of all zooplankton taxa examined increased from 2017 to 2018, indicating an increase in the nutritional quality of the prey field utilized by larval and juvenile fish in Icy Strait, northern southeast Alaska (p. 74).
  • Nearshore intertidal ecosystem components of the western Gulf of Alaska in 2017 had reductions in fucus algae (habitat for mussels), mussel density (prey of sea stars), and sea star abundance (predators) from western Prince William Sound to the Alaska Peninsula, except for a large increase in mussels in Kenai Fjords (p. 61).
  • In 2017, abundances for most larval fish surveyed in the western Gulf of Alaska returned towards average levels following the 2014–2016 marine heatwave, but remained low for the ronquils, Pacific cod, starry founder, and northern lampfish (p. 76).
  • Herring, sand lance, and sablefish were prevalent in black-legged kittiwake diets in 2018 at Middleton Island. Sand lance constituted about 50% of the forage fish fed to auklet chicks, continuing an increasing trend in proportion of diets since 2013 (p. 77).
  • A new indicator presents a 6-year time-series of energy density of 5 pelagic life stages of salmon and groundfish species. In 2017, energy density was below average for young-of-year sablefish, juvenile Chinook salmon, and juvenile pink salmon, and above average for young-of-year pollock and arrowtooth flounder in the eastern Gulf of Alaska (p. 81)
  • Herring biomass in Prince William Sound remains low after the steep decline in the early 1990s. In 2018, the observed mile-days of milt from spawning herring declined to the lowest level over the 1974–2018 period (p. 84).
  • Although the two largest and most consistent herring stocks in southeast Alaska—Sitka Sound and Craig—have declined substantially from their peaks of 2009 and 2011, respectively, they continue to be at levels well above the thresholds necessary to allow commercial fisheries (p. 85).
  • In nearshore waters of Icy Strait in northern southeast Alaska during 2018, juvenile and adult salmon catch rates were among the lowest since the survey began in 1997 (p. 89).
  • In the same Icy Strait survey, juvenile salmon length and weight were below average in 2018 relative to the 21-year time series. Energy density values declined in 2017 relative to 2016, but have been at or above the long-term mean since 2014 90).
  • Low marine survival and a record low number of adult pink salmon returns to Auke Creek weir in 2018 indicate poor conditions for survival in the Gulf of Alaska during the summer and winter of 2017 (p. 92).
  • The second lowest and lowest marine survival rates since 1980 were recorded for age-1 ocean and age-0 ocean coho salmon, respectively, returning to the Auke Creek weir in 2018. These indicate poor conditions for survival in the Gulf of Alaska from the summer of 2017 through the summer of 2018 (p. 95).
  • Arrowtooth flounder, flathead sole, and other flatfish continue to dominate the catches in the ADF&G trawl survey off Kodiak, but not to the same degree as seen in previous surveys. A sharp decrease in overall biomass is apparent from 2007 to 2017 from the years of record high catches occurring from 2002 to 2005. There was a slight increase in total biomass in 2018 (p. 97).
  • In 2018, survey catch rates for arrowtooth flounder, flathead sole, Pacific cod, Pacific halibut, and skates were below average. Above average anomaly values for Tanner crab in 2018 were due to a large increase in numbers of juvenile crab captured in both inshore and offshore areas that have not been observed for several years (p. 97).
  • Fish-eating seabirds in the Gulf of Alaska had generally normal reproductive success at monitored colonies in 2018. Murres had better colony attendance and fledging rates that during 2015–2016, but the overall numbers of breeding birds was still low. Timing of breeding was normal for most species at Chowiet (Semidi Islands), late for murres at East Amatuli (Barren Islands), and late for murres and gulls at St. Lazaria (Southeast Alaska)( p. 102).
  • Humpback whale calving and juvenile return rates in Glacier Bay and Icy Strait declined substantially beginning in 2015. Crude birth rates remained anomalously low from 2016–2018. These changes in calving and juvenile return rates may be related to recent changes in whale prey availability and/or quality, which may in turn be negatively affecting maternal body condition and therefore reproductive success and/or overall juvenile survival (p. 105).
  • The 8th fall survey of whales in Prince William Sound found the second lowest number of humpback whales (n=17), lack of whale/herring hotspots, low acoustic signals for pollock and krill, and low numbers of humpback whales, marine birds, herring, and forage fish relative to earlier surveys (p. 107).
  • Stellar sea lion pup counts declined in the eastern and central Gulf of Alaska population from 2015- 2017. Non-pup counts remained stable in the western population but declined in southeast Alaska (p. 108).
  • A new indicator demonstrates that the stability (inverse biomass coefficient of variation) of groundfish biomass has been relatively constant from 2007–2017. Stability decreased slightly in the Western and remained relatively constant in the Eastern Gulf of Alaska from 2015 to 2017 (p. 111 and 115).
  • A new indicator tracks fluctuations in the size of groundfish sampled over time by the Gulf of Alaska bottom trawl survey. The mean length of the groundfish community in the Western and Eastern Gulf of Alaska has generally been stable over the years 1984–2017. Fluctuations are largely the result of variation in the biomass indices of forage species, such as herring, that are not well sampled by the bottom-trawl (p. 112 and 116).
  • A new indicator tracks the mean life span of the groundfish sampled by the Gulf of Alaska bottom trawl survey over time. This indicator serves as a proxy for the mean turnover rate of species and communities” and is intended to reflect ecosystem stability and resistance to perturbations. The metric has been largely stable over the time period with some interannual variation due to high biomass estimates of short-lived species such as herring (p. 113 and 117).
  • The prevalence of Ichthyophonus infections in sport-caught Pacific halibut landed at Homer increased from 19–59% from 2011–2017. Despite the high infection prevalence, there was no indication that the parasite caused serious damage to the host; thus it appears that Ichthyophonus can occur at high infection prevalence with concomitant low infection intensities in Pacific halibut (p. 119).