Zooplankton Bongo Net Data from the 2019 and 2020 Gulf of Alaska International Year of the Salmon Expeditions

Study Extent

Zooplankton were collected with a bongo net at 58 stations throughout the Gulf of Alaska (GoA), weather conditions permitting, between February 19 - March 15, 2019, and at 36 stations between March 13 – April 5, 2020.

Sampling

Zooplankton were collected using a bongo net at each station after the CTD and water sampling, weather and oceanic conditions permitted. The bongo net (3 m length, 250 µm mesh, 50 cm diameter) was deployed to a depth of 250 m and retrieved vertically at 1 m s-1. Volume filtered was determined using General Oceanics flowmeters and by multiplying effective distance travelled by the mouth area. After the bongo net deployment and recovery, the net was rinsed down into the cod end. Samples from one cod end were rinsed into a jar and preserved in 4 % formaldehyde for future taxonomic analysis. The other cod end was rinsed into a sieve and transferred below deck where it was subsequently size fractionated (250-500 µm, 500-1000 µm, 1000-2000 µm, 2000-4000 µm, and >4000 µm) onto pre-weighed filters. Individuals larger than 4000 µm were measured, identified to species level, and stored in individual Eppendorf tubes. Size fractionated zooplankton samples were stored on dry ice.

Method steps

1. Zooplankton taxonomic analysis was conducted based on previous methodology instituted by the Institute of Ocean Sciences. Zooplankton were transferred from the formalin solution and rinsed with tap water. Samples were initially processed by identifying all organisms > 10mm in length and subsequently identifying all organisms between 5 mm and 10 mm in length. Samples were then subsampled using a box plankton splitter. All individuals in the subsample were identified to the lowest taxonomic level possible (i.e., species, life stage, and sex when possible). For each species identified a type specimen was photographed and catalogued. Volume filtered was calculated by using the General Oceanics flowmeter data from the net tow, and each net tow was subsequently compared to its depth-estimated volume. If the flowmeter value was > 50 % different from the depth-estimated value we considered this a flowmeter failure and the depth-estimated volume was used, as is standard practice by the Hakai Institute and the Institute for Ocean Sciences.

Gulf of Alaska