AI_Assessment
Aleutian Islands 2024 - Noteworthy Topics
We include information here that is deemed of relevance to ecosystem considerations of fisheries managers, but does not fit our typical indicator format. Information included here is often new, a one-time event, qualitative, some other type of non-standard ecosystem indicator, or a deeper discussion on a topic of interest
School closure at Adak and school enrollment trends
The school at Adak closed last year after initial low enrollment (5 students). This follows the previous closure of the school at Nikolski in 20103. Enrollment at small communities has a slow decreasing long term trend, with the exception of Akutan. Alaska requires public schools to have a minimum of 10 students enrolled to qualify for state funding. Communities in the Aleutians tend to have a significant portion of their economic activity dependant on fisheries. The SSC has highlighted the relevance of Adak as the only port for emergencies and supplies in the western Aleutians. The community of Adak lost one of its main economic activities and employers after the fish processing plant closed in 2020. Lack of schools pose a challenge for families to stay at or move to Adak (or other small communities), favoring temporary residents as opposed to year-round/ permanent residents that can further support the local economy.
Figure 7: Total KG-12 enrollment at schools in the Aleutian Islands (west of False Pass).
Contributed by: Ivonne Ortiz1,
1Cooperative Institute for Climate, Ocean, and Ecosystem Studies,
University of Washington, Seattle, WA
Gradients in diets and prey trends along the Aleutian Islands
Based on regional diets of Pacific cod presented last year, we take a closer look this year at survey data for prey items and current fish condition. Last year, as part of a preliminary analysis, we found the ratio of fish to invertebrate prey in diets has changed from a majority of fish in the early portion of the time series to a majority of invertebrates in the later portion. The trend however, appears to not be driven by an increase in invertebrate prey populations but rather a decrease in the availability of fish and lack of other fish prey substituting the decrease of Atka mackerel in Pacific cod diets (Ortiz and Zador, 2023).
Pacific cod diets can be further used as a case study of prey availability along a longitudinal gradient. We take a preliminary look at the combined biomass of Atka mackerel and pollock by region, as estimated from survey data, to look for correspondence between prey biomass, total prey weight consumed as a proportion of predator weight, fish condition, and bottom temperature (Figure 8). The combined biomass of pollock and Atka mackerel (prey biomass) follows similar trends to that of total prey weight as percent of predator weight, in the western and central Aleutians, but increasingly differs towards the east. This highlights the relevance of other prey such as shelf demersal fish (e.g. poachers and sculpins), squids, and shrimps. Survey estimates show an overall decreasing trend of miscellaneous benthic species: eelpouts, poachers, shrimp and sea stars, with eelpouts and shrimps decreasing particularly in the western Aleutian Islands. Fish condition appears to increase when fish eat at least 1% of their weight, but not always – which suggests the caloric value of the prey varies and can offset lower consumption rates or vice versa.
Pacific cod diets can be further used as a case study of prey availability along a longitudinal gradient. We take a preliminary look at the combined biomass of Atka mackerel and pollock by region, as estimated from survey data, to look for correspondence between prey biomass, total prey weight consumed as a proportion of predator weight, fish condition, and bottom temperature (Figure 8). The combined biomass of pollock and Atka mackerel (prey biomass) follows similar trends to that of total prey weight as percent of predator weight, in the western and central Aleutians, but increasingly differs towards the east. This highlights the relevance of other prey such as shelf demersal fish (e.g. poachers and sculpins), squids, and shrimps. Survey estimates show an overall decreasing trend of miscellaneous benthic species: eelpouts, poachers, shrimp and sea stars, with eelpouts and shrimps decreasing particularly in the western Aleutian Islands. Fish condition appears to increase when fish eat at least 1% of their weight, but not always – which suggests the caloric value of the prey varies and can offset lower consumption rates or vice versa.
There might be a potential decrease of prey availability for predators feeding on fish or a combination of fish and invertebrates. The apparent decrease in prey highlights some of the challenges to apex foragers, not factoring increasing temperatures which also seem to coincide with lower fish condition. Food-webs in the Aleutian Islands tend to have an east-west gradient where food-webs in the east are more piscivorous and neritic while in the west they are more planktivorous and oceanic. The increase of rockfish abundance in the west, while bringing stability, reduces the amount/ quality of fish prey as well as the availability and timing of fish eggs and larvae to a variety of predators, as most rockfish are live bearers. In the Aleutians, Pacific ocean perch undergo parturition in April (TenBrink and Spencer, 2013) as opposed to gadids which hatch earlier in the year (e.g. cod spawns February to April, Neidetcher et al. 2014) and Atka mackerel spawn from July through mid-October with peak hatching in late November (McDermott et al., 2007; Lauth et al., 2007). A more holistic study is needed to evaluate the impacts on apex predators of a shift in the primary traits, phenology, and life history strategies within the pelagic foragers guild in the Aleutian Islands.
Contributed by: Ivonne Ortiz1, Kerim Aydin2, Rebecca Howard3, Bianca Prohaska3, Ned Laman3, Sean Rohan3, Christina Conrath3, and Susanne McDermott3
1 Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington, Seattle, WA
2 Resource Ecology and Fisheries Management, Alaska Fisheries Science Center, NMFS, NOAA
3 Resource Assessment and Conservation Engineering Division, Groundfish Assessment Program, Alaska Fisheries Science Center, NMFS, NOAA
Figure 8: From left to right Western, Central, Eastern Aleutians, and Southern Bering (NMFS areas 543, 542, 541, and 518-519 respectively). From top to bottom: graphical summary for each region of (row 1) Pacific cod diet and total prey consumed as percent of predator (row 2) prey biomass (Atka mackerel and pollock) vs total prey consumed as percent of predator (Pacific cod) weight, (row 3) fish condition and (row 4) mean annual bottom temperature above or below timeseries mean.
3http://education.alaska.gov/data-center