During the first quarter of 2009, fisheries observers collected 556 stomach samples from the eastern Bering Sea. In the laboratory, Resource Ecology & Ecosystem Modeling (REEM) Program staff analyzed 1,704 stomach samples from seven predator species. In total, 3,399 records were added to the REEM food habits database.
By Troy Buckley, Geoff Lang, and Mei-Sun Yang
Alaska Marine Science Symposium Presentations
- Resource Ecology:
Todd TenBrink attended the Alaska Marine Science Symposium in Anchorage, Alaska, in January to present a poster detailing studies of age, growth, maturity, and food habits of five sculpins—plain sculpin (Myoxocephalus jaok), great sculpin (M. polyacanthocephalus), warty sculpin (M. verrucosus), yellow Irish lord (Hemilepidotus jordani), and bigmouth sculpin (Hemitripterus bolini) -- in the eastern Bering Sea and Aleutian Islands.
Filling life history data gaps will aid in assessing sculpin stocks and help to better understand their ecological role in these regions. The break and burn method for otoliths was used to age all species, with the exception of the yellow Irish lord, which was aged using thin sectioning.
Maximum ages (years) are as follows: yellow Irish lord (28), bigmouth sculpin (20), warty sculpin (18), great sculpin (17), and plain sculpin (16). In each species, sex-specific von Bertalanffy growth curves were derived and were found to be statistically different.
This study was the first to report on the ageing of the warty and bigmouth sculpins, and estimated maximum ages for the yellow Irish lord, great sculpin, and plain sculpin are the highest reported. Maturation was investigated based on histological methods, and analyses are being conducted for great sculpin, yellow Irish lord, and bigmouth sculpin.
Length and age at 50% maturity for the yellow Irish lord for the eastern Bering Sea and Aleutian Islands was estimated to be 26.1 cm (3.4 years) and 28.9 cm (5.0 years), respectively. Maturity estimates were also reported for the great and bigmouth sculpins in the eastern Bering Sea.
- Multispecies Modeling:
Stephani Zador attended the Alaska Marine Science Symposium and presented a poster focusing on potential distributional shifts in overlap between arrowtooth flounder and walleye pollock in the Bering Sea. The work identified physical and biological habitat characteristics that are correlated with arrowtooth flounder biomass trends sampled at individual trawl stations and found that small-scale regions within the eastern Bering Sea shelf have contributed unequally to the overall rapid increase in abundance of arrowtooth flounder.
Applying the hierarchical k-medoids clustering technique to arrowtooth catch-per-unit-effort data revealed four distinct spatial groups showing stable, increasing, and variable trends. Catch rates in high-density areas near the shelf break have remained stable since the early 1990s while catch rates have increased to the northwest and east.
Annual changes in range expansion and contraction are negatively correlated with the extent of the cold water pool on the Bering Sea shelf. Age-1 and age-2 pollock comprise the majority of arrowtooth diets in all areas, but higher rates of nonempty stomachs in the northwest region indicate that predatory impacts on pollock may be higher there.
This analysis will provide information about the potential for arrowtooth flounder to further increase their distribution and abundance in the Bering Sea and help to predict future responses to climate and fisheries management actions.
- Ecosystem Modeling:
Ivonne Ortiz attended the Alaska Marine Science Symposium and presented a poster describing FEAST (Forage-Euphausiid Abundance in Space and Time), a multispecies bioenergetics model for forage and predatory fish species linked to NPZ (Nutrient-Phytoplankton-Zooplankton) and ROMS (Regional Ocean Modeling System) for the northeast Pacific and Bering Sea at a 10-km resolution that is part of the Bering Sea Integrated Research Program (BSIERP).
The FEAST models includes nine fish species (walleye pollock, Pacific cod, arrowtooth flounder, salmon, capelin, herring, eulachon, Pacific sand lance and myctophids) which have a two-way interaction with the seven zooplankton groups in the NPZ model (small/large microzooplankton, small/large copepods, euphausiids, jellyfish, and benthic infauna). Additionally, temperature and advection from the ROMS model are used in the bioenergetics and movement components.
The operating hypothesis in FEAST is that forage fish and macrozooplankton (e.g., euphausiids) are tightly coupled in a two-way interaction, and the dynamics of this interaction under different climate scenarios is a strong structuring element for the ecosystem as a whole. For example, variation in late summer prey supply may affect the fall diet transition of predatory fish switching from plankton to fish, affecting the year-class strength of multiple species and overall availability of forage species within the ecosystem.
Retrospective data analysis provides some basic parameters and initial conditions for FEAST. Data for feeding patterns is from the Food Habits database maintained by the REEM Program. FEAST will also make extensive use of data collected by other BSIERP projects, particularly those related to acoustic surveys, fish distribution, and functional foraging responses.
FEAST itself will ultimately be incorporated into economic and spatial fishery predictions, as well as into management strategy evaluations which are also part of BSIERP.
By Todd TenBrink, Stephani Zador, Ivonne Ortiz, and Kerim Aydin
