# PREDATOR WORKING GROUP REPORT

## First U.S. Southern Ocean GLOBEC Science Investigator Meeting
Arlington, VA
25-26 May 2000

## Dan Costa, Working Group Chair

## Science Question:

The predator working group will relate the behavior of marine mammals and seabirds relative to the distribution and abundance of krill and the factors that result in krill being an optimal prey item. These data will be used to model rates of krill predation by birds and mammals in the study area. The behavior and distribution of predators is determined by an interaction between the availability of krill and its quality (energy content). Mammals and birds feed on krill aggregations that result from an interaction between krill behavior and physical forcing (ice, water column processes). Our goal is to understand the relationship between physical and biological factors that affect the behavior of top predators in relation to their predation on krill.

## Implementation:

Studies on predator will employ two approaches to integrate large-scale processes with individual based behavior. Visual and acoustic surveys will be carried out to establish the overall pattern of distribution between predators, krill and the oceanography. These data will be coupled with data on the foraging behavior of individual animals captured on the ice. The surveys will be carried out as part of the overall broad area survey, while the individual based studies will be part of the process cruise. Marine mammals and seabirds operate at a scale intermediate between that which will be sampled under the large area survey and process studies. Therefore integration of data acquired from the broad area survey and the process studies will require focal surveys that can be carried out at a finer scale to define the dynamics of individual krill aggregations.

## Visual survey:

During daylight two independent visual survey teams will record marine mammal and seabird distribution. Chris Ribic will focus on seabirds, but will also record seal and cetacean data. Standard line transect methods will be used with a transect width of 300 m on either side of the vessel. The team will consist of two observers operating from the bridge of the survey vessel.

A survey team, consisting of 2 observers from the IWC (International Whaling Commission) will focus on cetacean distribution and abundance. They will employ high power mounted binoculars (Big Eyes) to extend the length of their transect. These observers will operate either from the flying bridge, in a specially constructed plywood hut, or in the Ice Bridge.

## Acoustic Survey:

The acoustic survey program will assess the abundance and distribution of vocalizing marine mammals by a combination of bottom mounted acoustic recorders and sonobuoys deployed during the broad area survey. The bottom mounted acoustic recorder will be deployed and recovered as part of the mooring cruise. Sonobuoys will be deployed as necessary to obtain continuous acoustic coverage during the broad area survey.

Surveys will be carried out in concert with the broad area survey. Upon completion of the broad area survey it will be necessary to carry out fine-scale surveys on a mesoscale level to provide information relevant to the scale of the predator. In order to better understand the ''choices'' employed by predators it will be necessary to sample representative krill aggregations where predators are both present and absent. These could be aggregations identified during the broad area survey, or areas where satellite tagged penguins and seals have been observed.

## Focal Animal Studies:

The movement and diving behavior of penguins and seals captured on the ice will be followed using satellite tags (penguins; Frazier) and satellite linked time depth recorders (crabeater seals; Costa, Burns, Crocker). Investigators will use Zodiacs to approach individual flows to capture and instrument animals. Diet will be quantified by stomach lavage (penguins), enema and collection of scats (seals). The size and sex of krill consumed by penguins can be readily determined from stomach samples. It is likely that the size and sex of krill consumed by seals can be assessed from carapace recovered in the scat. These data will allow a comparison of whether seals and penguins are targeting particular size class of krill or they are just taking what is available. An additional measure of the diet of seals will be acquired by comparing the free fatty acid and stable isotope profiles in the blubber of predators and prey (Bill we could also do this on penguins, all it takes is a blubber sample?).

Twelve crabeater seals will be instrumented each year with satellite linked time depth recorders (SLTDR) and X Adelie penguins will be equipped with location only satellite tags. A group of penguins will be tagged during February at Palmer Station and will provide data prior to the first cruise. An additional group of penguins will be instrumented during both cruises. SLTDRs are capable of providing data on the location and diving pattern of individual seals until February of the following year (Tags fall off when the animal molts). Seal tags may also provide water column temperature information.

## Data required from other groups:

The predator studies will be dependent on the other groups for information on krill distribution and abundance as well as the physical oceanography. As such it is anticipated that we will use these data as they become available with the assistance of the other working groups. However, we have some specific needs that deserve particular consideration.

## Diet:

Data on the size and sex of krill in the study area will be needed along with information on it's proximate composition and energy content. Data on the abundance of alternative prey (fish) and its composition would also be valuable to assess the factors that regulate prey choice in top predators.

Frozen samples of representative krill and fish will be required for analysis of free fatty acid and stable isotope signatures. These samples will be returned to UCSC/ UAA for analysis.

## Issues:

The visual and acoustic surveys are ideally suited for the overall broad area survey. Data are acquired while underway during daylight hours for the visual work and 24 hrs a day for the acoustic work. Data predator hot spots collected during the initial broad area survey can be used to suggest sites to be revisited on the 2nd half of the survey.

Focal animal studies are problematic in that although their focus is on predators foraging within the survey grid animals can only be captured on the ice where people can safely operate. For this reason it is anticipated that this work will take place as part of the process cruise. However, predators are patchily distributed and may disperse after capture of one or more individuals. Therefore careful consideration must be given to selection of sites where the process vessel will be on station for multiple days. Ideally process stations would have an abundance of top predators, krill and ice. Further, as data collected from instrumented animals can be used to direct fine scale sampling it will be advantageous to instrument animals early in the cruise.