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Department of Fisheries Oceanography - MS Thesis Defense
- Location: > See description for location
- Contact: > See Description for contact information
- Description: The School for Marine Science and Technology
Department of Fisheries Oceanography
MS Thesis Defense
"A Video Trawl Survey for Atlantic Cod (Gadus morhua) in New England"
by Nicholas M. Calabrese
advisor
Dr. Kevin D. E. Stokesbury
Monday, May 14, 2018
9:00 am
SMAST East, Rooms 101/102
836 S. Rodney French Blvd, New Bedford
Abstract:
The Gulf of Maine Atlantic cod stock has been declining over recent decades restricting the commercial quota, and inhibiting fisherman’s ability to reach their quota of other healthy stocks in the Northeast multispecies groundfish fishery. In recent years there has been a disconnect between the observations of the fisherman, who are catching large amounts of cod, and the fisheries-independent trawl surveys, that are reporting declines in their cod catch indices. In collaboration with members of the fishing industry, we have developed a survey system that utilizes a live feed video camera mounted inside the codend of a demersal trawl net, with the goal of collecting high resolution distribution and abundance data on cod in the Gulf of Maine. This system can be towed with the codend open allowing fish to be recorded, identified, and quantified as they pass through, or closed allowing the collection of biological information and verification of video observations. Three field trials (winter 2016, winter 2017, and spring 2017) were conducted in the Gulf of Maine to survey Atlantic cod (Gadus morhua). To evaluate the use of this survey technique on Gulf of Maine cod we used the 68 hours of video collected and tested the following null hypotheses were tested: (1) the number of cod counted from the video and in the catch are similar; (2) the number of cod counted by sampling the entire video and subsampling the video are similar; and (3) the distribution of cod along the path of each tow is uniform. The first null hypothesis was accepted as there was no significant difference in cod counted in the catch and from the video. A generalized linear model showed that visibility impacted this relationship. The second null hypothesis was accepted as high intensity systematic subsampling produced the similar estimates of total catch. It was also best suited to sampling the aggregated distribution of cod in the tow path. However, for tows with a low density of cod, subsampling may grossly overestimate the number of fish. The third null hypothesis was rejected as the distribution of cod appeared to be aggregated when the tow path was divided into one-minute increments. Overall these results suggest that the video trawl system is an effective method of collecting abundance and distribution data, and could provide a minimally invasive method of surveying aggregations of cod in the Gulf of Maine. In conjunction with the existing fisheries independent surveys, this data could strengthen the assessment of the cod stock.
For additional information, please contact Sue Silva at s1silva@umassd.edu.
- Topical Areas: School for Marine Sciences and Technology, SMAST Seminar Series
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