Study of Seasonal Resident Gray Whales Feeding Strategy in N. Puget Sound, WA, in 2016 Contract Report for Cooperative Agreement CA-16-320

This report summarizes research conducted in 2016 examining gray whale occurrence and feeding in northern Puget Sound by Cascadia Research under a cooperative agreement from the Washington Department of Natural Resources (DNR). This is the 2nd year of expanded research conducted on this topic. The DNR Aquatics Lands Program is implementing an adaptive management research approach to understand impacts from human activities that influence habitat and species on state owned aquatic lands (SOAL). Ghost shrimp have been harvested historically from areas around Saratoga Passage to be used as live fishing bait. According to Washington Department of Fish and Wildlife estimates, the commercial harvest of ghost shrimp totals more than 50 tons annually. DNR suspended harvesting on DNR lands in April 2014 over concern about impact of the harvest on gray whales and concerns raised by local residents. Estimates of biomass of ghost shrimp on DNR lands were just over 9,000 Metric Tons in 2015 with the harvest representing about 20 Metric Tons (Pruitt and Donoghue 2015). These findings prompted DNR to lift the moratorium on harvesting.

Around northern Puget Sound (NPS) a small but stable group of gray whales return seasonally primarily from March to May to feed prior to continuing their northern migrations (Calambokidis et al. 2002, 2010, Weitkamp et al. 1993). These whales have been individually identified and cataloged by Cascadia Research and a core group of just under a dozen of these individuals are documented returning each year including some of the individuals in the first years of directed research (1990 and 1991). One of their primary prey has been documented to be ghost shrimp in intertidal areas and they can be observed feeding at high tide in intertidal areas where there are dense aggregations of prey. While their feeding on ghost shrimp has been documented there is little quantitative data on which to calculate their consumption of ghost shrimp or the relative importance of this prey items.

Dedicated work to examine the feeding of gray whales on ghost shrimp to assist DNR began in 2015 (Pruitt and Donoghue 2016, Calambokidis 2016). The project would address a number of objectives related to key elements required to address gray whale consumption and reliance on ghost shrimp in the northern Puget Sound region. The following activities were conducted in 2016:

1. Continue sighting surveys and individual identification of gray whales to identify the number and timing of individuals present to evaluate changes in use of this region over time. Conduct surveys during at least three different periods during the spring to document feeding locations as well as put trained observers on whale watch boats to get supplemental sighting and photo-ID data.

2. Deploy and recover video tags in association with the above effort to document detailed feeding behavior and locations to allow better assess proportion of feeding on intertidal ghost shrimp versus other prey and number feeding events on ghost shrimp. Deployments would target three time periods during the spring to better sample the entire period and region.

3. Collect feces of gray whales during above activities to identify prey items and proportion of diet attributable to ghost shrimp.

4. Compare occurrence in 2016 with past years to examine changes in number of animals, duration, and locations of feeding.

Some of the key preliminary results from some of this research are summarized below with figures or tables highlighting some of the findings. While analysis of this data is still underway, we summarize key results below.

Citation:

Calambokidis, J. 2016. Study of Seasonal Resident Gray Whales Feeding Strategy in N. Puget Sound, WA, in 2016 Contract Report for Cooperative Agreement CA-16-320.