Dataset: shrimp bycatch - modified otter trawls

Name: Comparison of Catch and Bycatch with the Addition of Escape Holes to Otter Trawl Nets in the Northeast Shrimp Fishery from F/V Ocean Reporter NEC-BL2003-2 in the Gulf of Maine from January to March 2005 (NEC_ProjDev project)
Published: 2006-07-01
Keywords: oceans

Cite This Dataset

Project:

Northeast Consortium: Project Development (NEC_ProjDev)

Program:

NorthEast Consortium (NEC)

Co-Principal Investigator:

Dr Alan Michael

Captain:

Bill Lee

Version:

final

Version Date:

2006-07-01

Validated:

Yes

Current State:

Final no updates expected

Comparison of Catch and Bycatch with the Addition of Escape Holes to Otter Trawl Nets in the Northeast Shrimp Fishery from F/V Ocean Reporter NEC-BL2003-2 in the Gulf of Maine from January to March 2005 (NEC_ProjDev project)

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Description

Comparison Of Catch And Bycatch With The Addition Of Escape Holes To Otter Trawl Nets In The Northeast Shrimp Fishery

Project Leader: Bill Lee, F/V Ocean Reporter

Final report

Small escape holes made from cut pieces of 6-inch PVC pipe were sewn into the net in front of the Nordmore grate in a standard shrimp net used in the northeast fishery. Preliminary tests had provided video of fish escaping through these holes during active trawling. A series of tows, with and without these holes in the nets were made from the vessels the Ocean Reporter and the Marina Rose. Seven other participating boats from Rockport, Massachusetts and Hampton, New Hampshire towed standard gear at the same time and in the same general area. Catch and bycatch was weighed and identified to provide a direct quantitative comparison of the percentage bycatch with and without the escape holes.

Mean catch rate for vessels using nets without rings was 235.5 lbs shrimp/hr with a bycatch rate of 16.7 lbs/hr or 6.6%. For the two vessels with escape rings installed in the nets, the catch rate was 228.6 lbs shrimp/hr with a bycatch of 27.5 lbs/hr or 10.7 %. The data was confounded by the large variation in bycatch rates among vessels and the limited number of tows. The experimental vessels encountered schools of pelagics (whiting or herring) on some days which heavily influenced results. One vessel, the Marina Rose appeared to show a significant reduction in bycatch rate from 19.4% without the rings to 9.4% with the escape rings installed. The other vessel, the Ocean Reporter had a bycatch rate of 7.5% without rings and 11.3% with the rings. A high catch of pelagics on several days during the tests with rings influenced results from this vessel.

A further complication to the study was a discrepancy in bycatch rates between vessels operating out of Hampton, New Hampshire and those out of Rockport, Masachusetts. The New Hampshire vessels had lower overall bycatch rates, which could be due to the area trawled, or performance of the gear. A similar study in the previous year had documented a lower catch of pelagics by the New Hampshire vessels. Future studies should involve a larger number of tows from one or two vessels.

Methods & Sampling

Rings from white PVC pipe were cut and installed in a standard otter trawl used to catch shrimp (Figure 1). This net was used in the normal commercial fishing mode. For each trawl (typically 2 - 3 hours) the location, depth, speed and duration of tow was recorded. At the end of each tow, the catch (lbs) of shrimp was evaluated and the bycatch identified, and weighed. Other vessels performed commercial shrimp operations in the same area at the same time using the standard otter trawl currently used by the fleet. Captains were offered a nominal fee to report catch and bycatch in the same manner. The data was converted into catch per unit effort and a comparison made, between the two trawls on catch rates and relative amounts and types of bycatch. A biologist met with respective captains to provide them with data sheets and instructions on the collection of data. These vessels operated in the same general area of Ipswich Bay and, in many cases, on the same day(s) as the Ocean Reporter.

Most tows were made in an area off Rockport Massachusetts at depths ranging from 56 to 76 meters. Three vessels out of Hampton, New Hampshire reported their catch from a little further north for a total of 13 boat/days. Average tow duration and speed for the fleet using the otter trawl was 2.2 hrs at 2.5 knots. On the Ocean Reporter, the trawl was towed at speeds from 2.5 - 3.0 knots for an average of 1.6 hours.

Data Processing Description

The data was summarized at ADM Associates, converted to catch-per-hour towed, and examined for differences in catch rates of shrimp and bycatch. Bycatch was separated into three categories; groundfish (hake, skates, flounders etc), pelagic fish (herring, whiting) and others (invertebrates such as starfish, crabs and scallops)

Data Files

File
shrimp_by.csv (Comma Separated Values (.csv), 3.77 KB) MD5:9b3e567563f39f1be64e5d87db792a22 Primary data file for dataset ID 3088

More Information about this dataset

Funding Sources

Funding Source	Award Number
National Oceanic and Atmospheric Administration	unknown NEC_ProjDev NOAA

Deployments

Deployment	Synonyms	Start Date	Platform	Investigator
NEC-BL2003-2		2005-01-04	F/V Ocean Reporter	Bill Lee (Chief Scientist) Dr Alan Michael (Co-Chief Scientist)	data info

Instruments

None available yet

Parameters

Date and time formats are described in python strftime() syntax.

Supplied Name	Supplied description	Supplied Units	Standard Name
modification	experimental treatment		no_bcodmo_term
date_local	local date		date_local
boat_name	vessel name		ship
no_of_tows	number of tows taken during cruise		no_bcodmo_term
time_towed	duration of tow	hours	time
wt_shrimp	weight of shrimp	pounds	weight
wt_shrimp_hr	weight of shrimp caught per hour	pounds per hour	weight
wt_bycatch	weight of bycatch	pounds	weight
wt_bycatch_hr	weight of bycatch per hour	pounds per hour	weight
pct_bycatch	percent of bycatch in the sample	%	no_bcodmo_term
wt_groundfish	weight of groundfish in sample	pounds	weight
wt_pelagic_fish	weight of pelagic fish in the sample	pounds	weight
wt_other_species	weight of other fish in sample	pounds	weight

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Dataset: shrimp bycatch - modified otter trawls