High-resolution Analysis of Groundfish Trawl Locations
in Central California.

Current Status of Accomplishment or Milestone: In progress: many maps have been made, analysis is underway and manuscript is being drafted.

Background: Mapping the locations of groundfish trawling can provide information on the spatial distribution of trawl effort and trawl caught groundfish. The resolution of trawl data before 1977 was 10-minute fishing blocks. Fisheries scientists and managers have been limited by the coarseness of this information and have wished for more detail. Actual locations of the start and end of each trawl have been collected since 1997, but were not mapped. Start and end points of trawling are currently available from 1997 to 2003 in an electronic database for California, but not for Oregon or Washington.

Purpose of Activity/Goal of Project: Test the usefulness of mapping individual trawls by endpoints, and analyze this technique for potential use by fisheries managers. Maps detailing distribution of trawling effort and species landed could be examined by fisheries managers to provide detailed information to the decision process for area closures. These maps could also provide information to decision makers on how past regulatory actions have affected the spatial distribution of fishing effort and catch.

Description of Accomplishment and Significant Results: Files of trawl logbooks matched to landings receipts were provided by the California Department of Fish and Game for 1997 to 2003. I used Microsoft Access to manage the data, and mapped it in ESRI ArcView using tools from ET Geowizard for steps that ArcView could not perform. Transforming the raw data into a map of the distribution of trawling requires many steps. Extensive quality control was performed, and about 5% of the original records were removed from the analysis based on trawl speed, location and species depth ranges. The catch and effort from individual trawls was summarized into 1 minute blocks for each year. This technique revealed areas of concentrated fishing effort in certain portions of the 10-minute blocks, and other areas with minimal trawling activity, and shifts in these areas over the years can be related to changes in fishing regulations. Other maps were created to display distribution of trawls by vessels’ port, depth distribution of fishing effort, and spatial distribution of individual species landed. Importantly, by overlaying the 1-minute distribution of the landings with the Rockfish Conservation areas, the maps illustrate the effectiveness of Council defined rockfish closure areas on the landings of species of concern.

Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): Demonstrates improvements in resolution and usefulness of trawling maps by using the start and endpoints of trawls and then summarizing effort and landings into 1-minute blocks. Distinguishes heavily trawled, lightly trawled and untrawled areas (at less than 2 km resolution) for each year from 1997 to 2003, which can be studied for cumulative impacts of trawling on habitat and to understand how regulatory actions influence the spatial distribution of catch and effort.

Problems: None.

Key Contact: Janet Mason (831-648-9028, Janet.Mason@noaa.gov).