Plankton tow data from nearshore coastal Washington State 2019-2020

Description

This dataset consists of plankton samples collected using a bongo-style net in northwest Washington state in summer and fall of 2019 and 2020. The objective of sampling was to document the availability and composition of prey species available to gray whales in the area. Sampling occurred monthly during the gray whale feeding season from June to November in 2019 and from June to September in 2020. There were seven sampling sites located in the Strait of Juan de Fuca and seven in the Pacific Ocean. Mysids collected in the samples were measured and the sex, length, species, maturity, and gravidity were recorded in the attached dataset. Non-mysids were identified to the lowest taxonomic level possible in 2019, but only to the family level if possible in 2020. A manuscript of our results will be submitted to PeerJ in January 2023.

Steps to reproduce

Mysid density was documented in northwest Washington State, from Chito Beach (48° 18.40’ N, -124° 25.39’ W) in the Strait of Juan de Fuca, west to Cape Flattery, and south to Ozette Island (48° 09.45’ N, -124° 45.39’ W) in the Pacific Ocean. To measure mysid density and composition, we conducted prey sampling at seven sites within the Strait of Juan de Fuca and seven sites in the Pacific Ocean (Figure 1 in Files). The number of sample sites visited was variable by month. All sample sites were close to shore in depths of less than 50 ft and were selected based on areas where gray whales have previously been documented to feed and a desire to stratify sampling sites throughout the study region. Exact sample locations moved closer or further from the shore throughout the season to consistently sample along the edge of the expanding and contracting kelp line. The South of Bodelteh Islands site was used in 2019 but was replaced by the Ozette Island site in 2020. Samples were collected using a Bongo-style net manufactured by Sea-Gear Corporation (Melbourne, FL, USA). Twin hoops measured 30 cm in diameter with a 3:1 mouth to length ratio and a 500-µm mesh. Sampling occurred monthly during the gray whale feeding season from June to November in 2019 and from June to September in 2020. At each site, the net was lowered over the side by hand until it reached the bottom, then was towed slowly (approximately 1 kt through the water, accounting for currents) near the bottom for 30 seconds and retrieved as fast as could be achieved by hand (approximately 0.6 m s-1). This procedure was repeated for two tows at each sample site, and contents of each tow were poured into a single 500-mL container. Samples were stored in 70% ethanol before processing. Mysids were identified to species according to Kathman (1986) using a 40x dissecting microscope. For samples collected in 2019, non-mysids were identified to the lowest taxonomic level possible using Shanks (2001). For samples collected in 2020, identification efforts focused on mysids, but other arthropods were still identified to the family group if possible. Mysids were measured from rostrum to telson, and the species, sex, maturity, and gravidity were recorded. Mysids were sexed based on the presence of a brood sac for females or a reproductive appendage for males, and the absence of either characteristic for a juvenile. Seven samples with high mysid density (>1000) were approximated by estimating the total count of mysids in the sample to the nearest 100 and using a 100-mysid sub-sample to characterize the demographics of the remainder. An additional three samples with high concentrations of non-mysids (Pinnotheridae zoea and Pleurobrachia bachei) were estimated to the nearest 100 individuals. Kathman RD, Austin WC, Saltman JC, Fulton JD. 1986. Identification manual to the Mysidacea and Euphausiacea of the northeast Pacific. Ottawa, Ontario: National Printers Inc.

Categories

Funding

Licence