Fishing / Shellfishing - Selective Fishing
Date Published: October 30, 2007
Number of Pages: 81
The first season of a pilot recreational mark-selective fishery for Chinook salmon (Oncorhynchus tshawytscha, “Chinook”) was implemented in Marine Catch Areas 11 (June 1-September 30, 2007) and 13 (May 1-September 30, 2007). These fisheries represent the first experience using mark-selective regulations for Chinook in these two south Puget Sound marine areas. Area 11 includes the marine waters from the north tip of Vashon Island to the northernmost Tacoma Narrows Bridge (Figure 1). Area 13 encompasses all marine waters south and west of the northernmost Tacoma Narrows Bridge (Figure 2). Mark-selective regulations in Areas 11 and 13 allowed for the retention of two adipose fin-clipped (“marked”) hatchery Chinook salmon of legal size (>22 in or 56 cm) per day, and required the safe release of all “unmarked” and/or sublegal Chinook salmon.
The pilot selective Chinook fisheries in Areas 11 and 13 were patterned after the pilot summer selective Chinook fishery in Areas 5 and 6 (WDFW 2007b) and the winter selective Chinook fishery in Areas 8-1 and 8-2 (WDFW 2007a and 2007c). WDFW has successfully implemented and monitored the Areas 5 and 6 and Areas 8-1 and 8-2 fisheries for the past five and two years, respectively.
The objectives of the Areas 11 and 13 pilot selective Chinook fishery were similar to those of the Areas 5 and 6 and Areas 8-1 and 8-2 selective Chinook fisheries: 1) to maintain or increase recreational fishing opportunity while accommodating the conservation goals defined for Chinook salmon under the Puget Sound Chinook Harvest Management Plan; and 2) to collect the data necessary for post-season fishery evaluation and future-fishery planning.
Survey design and field methods
We implemented an intensive sampling design during the Area-11 selective Chinook fishery (June 1-September 30, 2007). This study design was built around Murthy’s population-total estimator (Murthy 1957; Cochran 1977) and was focused specifically on obtaining daily estimates of catch and effort. Area-11 sampling incorporated comprehensive and complementary data collection strategies, including: dockside angler interviews (with catch sampling), on-the-water (instantaneous) effort surveys, test fishing, and voluntary trip reports (VTRs) provided by charter boats and private anglers. Using data emerging from this design we estimated: the total number of salmon encountered (i.e., retained and released) by anglers during the fishery and its species, size [i.e., legal (>22 in or 56 cm) vs. sublegal], and mark-status[i.e., marked (adipose-fin clipped) vs. unmarked (unclipped)] composition; total fishing effort; and total fishery impacts (i.e., mortalities, inclusive of estimated release mortality) by size/markstatus group. Based on test fishing data, we also report on biological attributes, such as length and age composition, of the “fishable” Chinook population targeted by anglers in Area 11. Finally, using coded-wire tag (CWT) recovery data, we estimated stock composition and, for double index tag (DIT) groups, we estimated total unmarked-DIT mortality due to the Area-11 selective fishery.
Data collection strategies for Area 13 included “Baseline Sampling” at fishery access sites (i.e., angler interviews and catch sampling within an opportunistic site-selection framework) and voluntary reporting of encounters and effort from private anglers. During dockside sampling, we enumerated effort, catch by species, encounters, mark rates (i.e., based on observed catch and reported releases, by mark-status group), and catch composition (i.e., based on CWT recoveries). Voluntary trip reports provided an additional means to estimate mark rates, encounter rates, as well Chinook encounter size composition (i.e., legal/sublegal proportions).
In this report we did not attempt to estimate total catch and effort in Area 13 or total impacts on Chinook due to the Area-13 selective Chinook fishery. Baseline information will be used in conjunction with the catch record card (CRC) system to compute post-season total catch and effort estimates for Area 13 (typically these estimates are available 1-2 years from the close of the fishery).
Area 11 Summary
For private boats fishing in the Area-11 fishery, we estimated that a total of 10,532 Chinook (10,414 marked and 92 unmarked) were retained in 78,771 angler trips, with an overall catch per unit of effort (CPUE) of 0.13 Chinook kept per angler trip. We estimated that anglers released a total of 28,716 Chinook (6,866 marked, 6,669 unmarked, 14,737 of unknown mark status, and 443 apportioned unidentified salmon). In addition, the known charter captain operating in Area 11 reported (via VTRs) taking 187 anglers (45 total chartered trips) fishing during the selective season, who in combination encountered 357 Chinook salmon; of these, 109 were kept whereas the remainder (248) were released. For private and charter vessels combined, anglers retained an estimated 10,641 (10,520 marked, 95 unmarked, 26 of unknown marked status) and released an estimated 28,964 (7,004 marked, 6,779 unmarked, 14,737 of unknown mark status, and 443 apportioned unidentified salmon) Chinook salmon, resulting in fishery-total encounters of 39,605 Chinook salmon.
Test fishers successfully replicated the fishing-method composition of the private fleet during their four months of sampling in Area 11. The test boat fished for a total of 485 hours during the Area 11 fishery and encountered a total of 292 Chinook salmon (153 legal, 139 sublegal). Based on test-boat encounters, we estimated mark rates at 75.2% for legal-size, 82.7% for sublegal-size, and 79.8% for all Chinook salmon. The size/mark-status composition of pooled (season-wide) test-boat encounters was: 39.4% legal-marked, 13.0% legal-unmarked, 39.4% sublegal-marked, and 8.2% sublegal-unmarked.
Anglers fishing from private vessels in Area 11 returned 74 Voluntary Trip Reports (VTRs) over the four-month fishery. In combination, these VTRs provided data on 129 angler-trips and details about 164 separate Chinook encounters (retained and released). Based on private VTRs, we estimated that 69.9% of legal-size, 71.4% of sublegal-size, and 70.7% of all Chinook encounters reported on VTRs were marked. Charter-VTR (69.4%) and test-boat catch data (75.2%) both yielded mark-rate estimates for legal-size Chinook that were comparable to those obtained via private-angler VTRs.
Samplers recovered a total of 334 coded-wire tags from Chinook harvested during the fourmonth selective Chinook fishery in Area 11. The majority of these (331) were Puget Sound stocks, while two tags were from California stocks and one tag was of Canadian origin. Sixtytwo CWT recoveries (19% of total) were from double index tags groups, with Chinook from Nisqually and Grovers Creek hatcheries contributing the most to DIT recoveries. Combining our sample rates and hatchery DIT release ratios, we estimated that anglers caught and released 238 legal-size, unmarked double index tagged Chinook, and that the mortality of unmarked legal-size double index tagged Chinook due to this selective fishery was 24 fish.
We applied and compared two methods for estimating total legal- and sublegal-size Chinook encounters due to the Area-11 selective fishery. For the first method (“Method 1”), we apportioned estimated total Chinook encounters (retained and released, from creel surveys) to the four size/mark-status categories of legal-marked, legal-unmarked, sublegal-marked, and sublegal-unmarked based on monthly test-boat encounter composition. As the number of Chinook encounters and its size/mark-status composition were known from charter reports, we added these counts to the private boat estimates to yield the total number of legal and sublegal Chinook encounters. Using Method 1, we estimated total encounters due to the Area-11 fishery at 39,605, which consisted of 10,283 retained legal-size fish (10,208 marked and 74 unmarked), 12,863 released legal-size fish (8,203 marked and 4,634 unmarked), 359 retained sublegal-size fish (338 marked and 21 unmarked), and 16,127 sublegal-size released fish (12,564 marked and 3,563 unmarked).
The second method (“Method 2”) for estimating the number of Chinook encounters is built on the assumption that anglers keep all legally harvestable (i.e., legal-size and marked) Chinook salmon encountered. Under Method 2, total encounters were estimated by dividing the number of legal-size marked fish that anglers retained by the proportion of legal-size marked fish in the targeted population (estimated from test-fishing data). Encounter estimates for the remaining three categories (legal-unmarked, sublegal-marked, sublegal-unmarked) were obtained by multiplying the estimated total by their test-boat proportions. Using Method 2, we estimated total a total of 22,313 Chinook were encountered in Area 11 during the selective fishery, which consisted of the same harvest composition as generated using Method 1 [i.e., 10,283 retained legal-size fish (10,208 marked and 74 unmarked), and 359 retained sub-legal fish (338 marked, 21 unmarked)] but substantially fewer estimated releases [11,672 total: 2,624 legal (0 marked, all unmarked) and 9,048 sublegal (6,988 marked, 2,060 unmarked)]. Given the different assumptions of the two approaches, we believe that the true number of encounters likely lies between Method-1 and -2 estimates; i.e., between 22,313 and 39,605 Chinook encounters.
We combined Method-1 and -2 Chinook retention and release estimates with legal (15%) and sublegal (20%) release mortality rates to estimate total fishery impacts. Based on Method-1, we estimated total Chinook mortalities due to the selective fishery at 15,792 fish, of which 1,503 were unmarked. Using Method-2 encounters, we estimated total mortalities at 12,884 Chinook, of which 901 were unmarked individuals. We believe the true number of mortalities likely lies between 12,884 and 15,792.
To place estimated impacts due to the Area-11 selective fishery into perspective, we compared the mortality range bounded by Method-1 and -2 estimates with pre-season management expectations (i.e., FRAM model run no. 3907). Based on this comparison, we observed notable differences between predicted and actual (estimated) mortalities for legal-marked Chinook, but negligible differences for all other size/mark-status classes (i.e., sublegal-marked and all (8,531 due to landed harvest, 4,710 due to post-release impacts; 1,704 unmarked, 10,997 marked) would occur as a result of the Area-11 fishery; whereas, we estimated that 12,884- 15,792 (range of Method-1 and -2 estimates) mortalities actually occurred for this group. Excess mortality was due to legal-marked Chinook retention. Our estimates of legal and sub-legal Chinook mortalities were less than or comparable to pre-season FRAM predictions for unmarked Chinook salmon. Altogether, these results suggest that the fishery operated within the conservation constraints defined during pre-season planning.
In terms of angler compliance with new selective regulations, creel-survey data showed that unmarked retention error (estimated total unmarked Chinook retained divided by total estimated unmarked Chinook encountered) was minor, at 1.4%. While preliminary reports from WDFW Enforcement staff corroborate this sampling observation, the Enforcement Program will present detailed results in a separate report. We believe the observed degree of angler compliance was due in part to the education efforts of our dockside sampling staff.
From May 1 through September 30, Area-13 dockside samplers observed a total of 444 Chinook (434 marked and 10 unmarked) based on 3,116 angler interviews. These observations on catch and effort yielded a season-wide CPUE of 0.14 Chinook kept per angler trip for Area 13. From interviews conducted during baseline sampling, anglers released 724 Chinook salmon (197 marked, 165 unmarked, and 362 with unknown mark status). When Catch Record Card data become available for 2007, these “Baseline Sampling” observations on Chinook retention and effort will be used to generate total estimates for these fishery parameters for the Area-13 selective season.
In addition to baseline observations, we acquired data on Chinook encounters and angling effort from VTRs returned by Area-13 anglers. In total, private anglers returned 21 VTRs during the Area-13 pilot selective Chinook season. These voluntary reports gave us information about an additional 42 angler trips encompassing 55 Chinook salmon encounters. In total, 52% of legalsize, 88% of sublegal-size, and 73% of all Chinook encounters reported on Area-13 VTRs were marked.
Samplers recovered 56 coded-wire tags from Chinook harvested in Area 13 during the fivemonth selective season. Fifty-five of these CWT recoveries were from Puget Sound stocks, and one was of Canadian origin. Six of these CWT recoveries were from DIT groups. In terms of angler compliance with newly implemented Area-13 selective regulations, creelsurvey data showed that unmarked retention error (estimated total unmarked Chinook retained divided by total estimated unmarked Chinook encountered) was minor, at 5.7%. While preliminary reports from WDFW Enforcement staff corroborate this sampling observation, the Enforcement Program will present detailed results in a future and separate report. We believe the observed degree of angler compliance was due in part to the education efforts of our dockside sampling staff.
Marine Areas 11 and 13 Selective Chinook Fishery, 2007 Post-season Report. Draft. October 30, 2007. Washington Department of Fish and Wildlife. Olympia, Washington.