Benthic studies adjacent to Sakhalin Island, Russia 2015 III: benthic energy density spatial models in the nearshore gray whale feeding area

Abstract

Energy densities of six dominant benthic groups (Actinopterygii, Amphipoda, Bivalvia, Cumacea, Isopoda, and Polychaeta) and total prey energy were modeled for the nearshore western gray whale feeding area, Sakhalin Island, Russia, as part of a multi-disciplinary research program in the summer of 2015. Energy was modeled using generalized additive mixed models (GAMM) with accommodations for zero-inflation (logistic regression and hurdle models) and regression predictions combined with kriging to interpolate energy densities across the nearshore feeding area. Amphipoda energy density was the highest nearshore and in the south whereas Bivalvia energy density was the highest offshore and in the northern portion of the study area. Total energy was the highest in mid-range distances from shore and in the north. Amphipoda energy density was higher than minimum energy estimates defining gray whale feeding habitats (312–442 kJ/m2) in 13% of the nearshore feeding area whereas total prey energy density was higher than the minimum energy requirement in 49% of the habitat. Inverse distance-weighted interpolations of Amphipoda energy provided a broader scale representation of the data whereas kriging estimates were spatially limited but more representative of higher density in the southern portion of the study area. Both methods represented the general trend of higher Amphipoda energy density nearshore but with significant differences that highlight the value of using multiple methods to model patterns in highly complex environments.

Benthic studies adjacent to Sakhalin Island, Russia, 2015 I: benthic biomass and community structure in the nearshore gray whale feeding area

“…This work contributes to a larger effort aimed at understanding impacts on western gray whales associated with seismic surveys during the 2015 summer and fall seasons (Aerts et al 2022). The benthic component includes three additional papers discussing long-term spatial-temporal trends in the benthic community (Blanchard et al, 2019), energy density of the benthic prey (Maresh et al 2022), and spatial regression modeling of dominant macrobenthos (Blanchard et al 2022).…”

Gray whale habitat use and reproductive success during seismic surveys near their feeding grounds: comparing state-dependent life history models and field data

“…Analysis of smaller 1-km 2 blocks indicated a higher density of gray whales farther than usual from shore in Cell 7 (Gailey et al, 2022b) which could have been related to a seasonal patch of high energy sand lance (Ammodytes sp.) (Blanchard et al, 2022a). Gray whales have previously been observed in that area feeding on sand lance (Fadeev, 2011).…”

“…In fact, density estimates from scan surveys indicated an almost complete lack of whales in the southeastern part of the nearshore foraging area (Cell 2). Inter-annual whale densities in the southern part of the nearshore area (Cells 1 and 2) have been highly variable since density data have been collected (Exxon Neftegas, 2018), with Cell 1 usually an area of lower prey biomass (Blanchard et al, 2019(Blanchard et al, , 2022a. Little is known about whale prey energy in Cell 2.…”

Seismic surveys near gray whale feeding areas off Sakhalin Island, Russia: assessing impact and mitigation effectiveness

“…The repeat sampling of the “historic” grid provided an indication of the prey availability in both feeding areas in relation to previous years and also served to document the long-term trend in prey availability (Blanchard et al, 2019 ). In addition, estimates of caloric content of main prey species were derived from selected samples taken in the nearshore and offshore feeding areas (Maresh et al, 2022 ), and spatial interpolation of prey data (Blanchard et al, 2022b ) provided prey variables for input into the gray whale behavior, distribution, and bioenergetics models.…”

“…The first part of this paper summarizes the mitigation approach, the second part summarizes the implementation of the mitigation measures during ENL’s seismic surveys, and the third part summarizes the overall strategy behind assessment of impacts and mitigation effectiveness. Results of this assessment, including western gray whale behavior and distribution responses to the 2015 seismic survey activities, availability of prey resources, and how a potential decrease of energy intake due to acoustic disturbance could affect reproductive success, are presented in separate papers within this special issue (Blanchard et al, 2022a , b ; Gailey et al, 2022a , b ; Maresh et al, 2022 ; Rutenko et al, 2022a , b ; Schwarz et al, 2022a , b ). It should be noted that ENL and SEIC implemented comparable but not identical mitigation measures; SEIC’s approach is summarized and discussed in IUCN ( 2015a , b , c , 2016 ) and is not part of this paper.…”