The Pacific Coast Feeding Group (PCFG) is a subgroup of the Eastern North Pacific (ENP) population of gray whales (Scordino et al. 2018). The ENP, a population of 24,000-26,000 individuals, migrates along the U.S. west coast from breeding grounds in the lagoons of Baja California, Mexico to feeding grounds in the Bering Sea (Omura 1988). The PCFG, currently estimated at 264 individuals (Calambokidis et al. 2017), stray from this norm and do not complete the full migration, instead choosing to spend their summer feeding months along the Pacific Northwest coast (Scordino et al. 2011). Since gray whales as a species already exhibit specialization (by being the only baleen whale that benthically forages) and since the PCFG display a second tier of specialization by not using the Bering Sea feeding grounds, it seems plausible that individuals within the PCFG might have individual foraging specializations and preferences. Therefore, my research aims to investigate whether individual gray whales in Port Orford exhibit individual foraging specializations. Individual foraging specializations can occur in a number of different ways including habitat type (rocky reef vs sand/soft sediment), distance to kelp, time and distance of foraging bouts, and prey type and density. For this class, my research question is whether prey quantity and/or community drives whale foraging.
The prey data has been obtained through zooplankton tow net samples from a research kayak in the summers of 2016, 2017, 2018 and 2019. Kayak sampling effort varies widely between the three years due to weather creating unsafe conditions for the team to collect samples. These samples have been sorted and enumerated to the zooplankton species level so that for each day when a prey sample was collected, we have known absolute abundances of prey species communities at each sampling station. Additionally, a novel GoPro method has been used to quantify relative zooplankton density at the same sampling stations.
The whale data is in the form of theodolite tracklines of gray whales that used the Port Orford study area during the summers of 2016, 2017, 2018 and 2019. Since whale tracking occurs at the same sites as prey sampling, we are able to map the prey community present at a particular location that whales forage at. The tracklines occur on a very fine spatial resolution as the study area is approximately 2.5 km in diameter, though some of the tracklines extend out to approximately 8 km offshore. Furthermore, as whales forage in the area, photographs are taken of each individual in order to match the trackline with a particular individual. This way, potential individual specializations may be detected if there are repeat tracklines of an individual. These tracklines have been analyzed using Residence in Space and Time, which assigns a behavior to each spatial point. The behaviors are broken down into three categories foraging, searching, travelling. Each of these behaviors is assigned a residual value (-1, 1, 0, respectively).
Gray whales will prefer areas with the densest prey, regardless of the community composition of prey found at different locations.
Daily interpolation layers will be created for prey density between the two sites, Mill Rocks and Tichenor Cove. These interpolations will then also be weighted according to the percentage that mysids and amphipods (the two main taxonomic prey groups) made up the community at each location. This will result in 3 layers per day: an overall interpolated prey density layer, an interpolated layer weighted by mysid abundance, and an interpolated layer weighted by amphipod abundance. Once these layers have been created, the RST analyzed whale tracks will be overlaid onto them. Statistical analyses (likely linear mixed models) will be used to determine whether overall prey density or specific prey communities drive gray whale foraging by relating the interpolated layers with the behavior residual values.
There will be many interpolated layers of prey density and weighted prey density. Furthermore, there could be some plots of overlaid tracklines showing where whales prefer to forage and search vs travel.
This spatial problem is important to science since genetic evidence suggests that there are significant differences in mtDNA between the ENP and PCFG (Frasier et al. 2011; Lang et al. 2014), and therefore it has been recommended that the PCFG should be recognized as being demographically independent. In the face of a proposed resumption of the Makah gray whale hunt as well as increased anthropogenic coastal use, there is a strong need to better understand the distribution and foraging ecology of the PCFG. This subgroup has an important economic value to many coastal PNW towns as many tourists are interested in seeing the gray whales. Therefore, understanding what drives their distribution and foraging habits will allow us to properly manage the areas where they prefer to forage.
I have novice/working knowledge of Arc-Info and Modelbuilder. I have never used Python before. I am proficient in R and image processing.
1a. What is A?
A is the behavior displayed by a gray whale at a certain location.
1b. What is B?
B is the density of prey as well as the weighted density of mysids and amphipods.
1c. What is the relationship you want to test between B and A?
Whether prey quantity and/or species drives whale foraging at a certain location.
1d. Why or how does B case/influence A? What is your hypothetical explanation for why or how B causes A (this is mechanism C)?
Gray whales, like most baleen whales, have a breeding season which they spend in warm waters and a feeding season which is spent in colder, more productive waters. For a subgroup of the Eastern North Pacific gray whale population, this summer feeding season is spent along the NW U.S. coastline (northern California, Oregon, Washington and southern British Columbia). The activities undertaken during each season is so distinct that no feeding is undertaken during the breeding season, and vice versa. As such, gray whales must regain 11-29% of critical body mass during the feeding season in order to prepare themselves for the breeding season during which they do not feed. Therefore, it seems logical to assume that their distributions and movements should be entirely dictated by where their zooplankton prey is and also, where it is the most abundant or most dense since their sole purpose during the summer is to feed.
1e. Now, write your question in this form: “How is [the spatial pattern of] A related to [the spatial pattern of] B via mechanism C?”
How is gray whale behavior (specifically foraging) related to the spatial pattern of prey density via optimal foraging theory.
Calambokidis, J. C., Laake, J. L. and A. Pérez. 2017. Updated analysis of abundance and population structure of seasonal gray whales in the Pacific Northwest, 1996-2015. Draft Document for EIS.
Frasier, T. R., Koroscil, S. M., White, B. N. and J. D. Darling. 2011. Assessment of population substructure in relation to summer feeding ground use in the eastern North Pacific gray whale. Endangered Species Research 14:39-48.
Lang, A. R., Calambokidis, J. C., Scordino, J., Pease, V. L., Klimek, A., Burkanov, V. N., Gearin, P., Litovka, D. I., Robertson, K. M., Mate, B. R., Jacobsen, J. K. and B. L. Taylor. 2014. Assessment of genetic structure among eastern North Pacific gray whales on their feeding grounds. Marine Mammal Science 30(4):1473-1493.
Omura, H. 1988. Distribution and migration of the Western Pacific stock of the gray whale. The Scientific Reports of the Whales Research Institute 39:1-9.
Scordino, J., Bickham, J., Brandon, J. and A. Akmajian. 2011. What is the PCFG? A review of available information. Paper SC/63/AWMP1 submitted to the International Whaling Commission Scientific Committee.
Scordino, J., Weller, D., Reeves, R., Burnham, R., Allyn, L., Goddard-Codding, C., Brandon, J., Willoughby, A., Lui, A., Lang, A., Mate, B., Akmajian, A., Szaniszlo, W. and L. Irvine. 2018. Report of gray whale implementation review coordination call on 5 December 2018.