Figure 1. Two schematic diagrams of competition
between top predators (shown here as a groundfish and a whale) and two prey
types (shown here as forage fish and krill). In (a), each predator
chooses separately from a range of prey, in which case the predator competition
is relatively indirect. In (b), each prey type forms local “hotspots” of
abundance, in which predators must compete directly for food.
Ecosystem Modeling
Assessing interactions between fisheries and marine mammals remains a critical national and international issue, and ecosystem models continue to enter this debate. In making policy decisions based on these models, it is important to evaluate the ecological assumptions underlying each model. For example, how do predators react to changes in prey in the model and in the real ecosystem?
In May, Kerim Aydin and Sarah Gaichas contributed a paper to the 2006 annual
meeting of the International Whaling Commission in St. Kitts, Caribbean Islands,
entitled “In defense of complexity: Towards a representation of uncertainty
in multispecies models.” In the paper, they described specific implications
of the scale of predator competition: do predators forage over separate areas,
each selecting from a range of prey choices (Fig. 1a) or do they compete
directly in local “hotspots” for
individual prey types (Fig. 1b)?
The answer may differ by predator, by ecosystem, or especially by local conditions.
Current multispecies and ecosystem models tend to make a single assumption
on the scale of competition and this may lead to biased results: the “complexity” of
predator/prey interactions discussed in the paper may be best evaluated by
using a wide range of statistically validated models and assumptions for any
particular predator/prey interaction.
By Kerim Aydin
Seabird Interactions
The AFSC’s Seabird Program focused on two types of seabird surveys during the
last quarter. The first is the stationary survey format developed by Washington
Sea Grant for longline cruises in 2004. This format was expanded to all AFSC
research and charter cruises conducted in 2006. Staff also coordinated with
the Northwest Fisheries Science Center to implement the surveys on its West
Coast charter cruises. That was accomplished and data are being collected throughout
the summer. These surveys now cover NMFS research and charter cruises from
southern California, up the West Coast, and throughout Alaska waters. The U.S.
Fish and Wildlife Service (USFWS) and many other clients have expressed great
interest in the results. Data from previous years are being analyzed and will
be made available to the public in the near future.
The second survey type is the strip-census. Staff have worked very closely with the USFWS Migratory Bird Division, Anchorage, Alaska, to support its North Pacific Research Board grant to conduct strip-census seabird surveys on appropriate platforms. The work will add to the extensive survey work completed in the 1970s and early 1980s and will ultimately be made available to researchers through the North Pacific Pelagic Seabird Database (www.absc.usgs.gov/research/NPPSD/index.htm).
Stephani Zador, Andre Punt, and Julia Parrish of the University of Washington
working under direction of the AFSC Seabird Program through funds provided
by the National Seabird Program are nearing completion of a risk assessment
of short-tailed albatrosses interactions with trawl vessels in the Alaskan
groundfish fishery. Stephani recently presented a talk, “Assessing the risk of endangered short-tailed albatross bycatch in the Alaskan trawl fishery” at
the Society for Conservation Biology meeting in San Jose, California.
