Albacore Commercial Fisheries

Albacore have been targeted by commercial fishermen based along the U.S. Pacific coast (California, Oregon, and Washington) for over 100 years. For the most part, formal monitoring programs for commercially harvested albacore have been in place since the early 1960s, i.e., a landing-receipt census program for tracking total catch, a port sampling program for evaluating biological characteristics of the landed catch (e.g., size and age distributions), and a fishermen logbook sampling program for evaluating important fishery descriptors used to assess the overall health of the stock (e.g., catch/effort statistics).

Troll Fishery

The U.S. troll fishery for albacore has operated along the West coast of North America since the early 1900’s. The National Marine Fisheries Service began collecting data from the fishery in 1974. Each year the SWFSC publishes a summary of the fishery and it’s associated statistics in an administrative report. 

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Landings

The commercial fleets that targeted albacore during the early 1900s used both pole-and-line ('live-bait' fishing) and troll ('artificial-jig' fishing) gears extensively. Other gears, such as longlines, purse seines, and drift gill nets have also been used over the years by commercial fishermen, but trolling operations have dominated since the early 1960s and now contribute over 90% to the total amount of albacore commercially landed each year. Generally speaking, troll, pole-and-line, purse seines, and drift gill net vessels operate in 'surface' fisheries that target 2-5 year-old fish (juvenile albacore) in the upper portions of the water column, and longline vessels operate in 'subsurface' fisheries that harvest 6 to 12 year-old fish (adult albacore) from deeper waters.

Documentation of landing statistics for North Pacific albacore harvested by U.S. fleets dates back to 1952. However, catch statistics prior to 1961 were not collected using rigorous monitoring programs and thus, we recommend an abbreviated time series that spans from 1961 to the present. Landings are primarily monitored via the processing facilities (canneries). That is, legal requirements dictate that financial transactions associated with commercially landed fish must be accounted for by a 'landing receipt.' Data from these receipts are processed and archived in a centralized database (Pacific Fisheries Information Network). Additionally, the Western Fishboat Owners' Association (WFOA-albacore fishing industry organization) monitors all landings of albacore and maintains an independent database. Final estimates of commercial landings of albacore are derived using both of the databases above. It is generally believed that a small amount of albacore are unaccounted for each year, given some fishermen do not sell their fish to a cannery, but rather, directly to the public (e.g., dockside from their vessel) and subsequently, may not document these sales.

Discard rates of non-marketable albacore are not known definitively, but limited 'observer sample' data from the U.S. North Pacific albacore troll fishery during the 1990s indicated that these rates are likely low and if accounted for, would not substantially inflate the estimates of the landed catch. In recent years, the troll fishery has generally discarded fish that are smaller than roughly 4.1 kg (58 cm or 2 yr-old fish).

Biological Distributions

Size distributions (fork length in cm) were developed from data collected through an ongoing port sampling program (1961-2000), i.e., fish are sampled at a processing facility after a boat has completed its fishing trip. For the most part, size data have been collected from the U.S. troll fishery; however, in some years, small numbers of samples from other fisheries (e.g., longline, pole-and-line, and gill net fisheries) have also been collected. The size- and age-distribution statistics presented here are based only on troll fishery samples.

Age distributions were developed from size data using straightforward age-slicing techniques (see Crone et al. 2000). Annual age distributions were derived by using a length-at-age relationship and visual evaluations of modal progressions to determine limits for size distributions within respective age classes, i.e., to determine the 'tails' of the distributions.

Catch-per-unit-effort Indices

As stated previously, beginning in 1961,  NOAA Fisheries' (previously the National Marine Fisheries Service) Southwest Fisheries Science Center began formal efforts to monitor the U.S. albacore troll fishery of the North Pacific Ocean. At this time, a standard logbook was developed, circulated to the fishermen, and collected (opportunistically) following completed fishing trips made by individual vessels that composed the U.S. albacore troll fleet. The logbook monitoring program has been conducted each year since 1961. Information maintained in the logbook has changed over the years; however, spatial/temporal and catch/effort data have been recorded in a similar fashion in every year. Over the last decade, approximately 10-30% of the total number of boat trips in a given year had corresponding logbook information available.

A logbook is generally maintained on a daily basis and sometimes even on a partial-day basis, and includes information pertinent to each day at sea over the course of an entire fishing trip. For example, a typical logbook contains daily records regarding where the vessel was (latitude and longitude) and for days when actually fishing, the number of albacore caught and discarded. Although a standard logbook and protocols are given to each fisherman, logbooks occasionally contain discrepancies and missing data. For the most part, returned logbooks contain complete records regarding days spent fishing (say versus days spent transiting to fishing areas).

Catch-per-unit-effort (CPUE), or the ratio of catch and effort, data from commercial fisheries have been used extensively to evaluate changes in abundance of exploited fish populations. The theoretical basis of such evaluations is that CPUE is proportional to average abundance, given the probability of catching fish ('catchability') is constant or if variable, can be appropriately adjusted ('standardized') in the analysis. A generalized linear model (GLM) is an effective tool for treating CPUE data, given this modeling approach provides a statistical framework for standardizing these data and exploring the extent to which different factors, such as spatial- temporal variables, technological advances in fish-finding and -catching equipment, and oceanographic conditions, influence catch and effort statistics that have been collected over time. For example, by incorporating year as a factor, the GLM generates estimates of annual standardized catch rate and its variance that can be generally interpreted as an index of stock abundance. See Crone et al. (2000) for methods used to develop the time series for standardized CPUE indices for albacore.

Age-specific Abundance Indices

For purposes of using an appropriate index of fishing success for 'tuning' a virtual population analysis of the North Pacific albacore stock, 'age-specific' abundance indices were developed using both biological (size- and age-distribution information), as well as commercial fishermen logbook sample data collected from the U.S. troll fleet. Ideally, auxiliary data components of a VPA-based model (e.g., the fish stock assessment model ADAPT) reflect indices of abundance that are age specific. The age-specific abundance indices are essentially the age-distribution data derived from the size data sampled from the U.S. troll fleet weighted by CPUE information using a spatial/temporal stratification in the estimation approach. See Crone et al. (2000) for methods used to develop the time series for age-specific abundance indices for albacore.