Observed Catch Tables - North Pacific Observer Program
Total catch of groundfish and halibut (retained and discarded) summarized by area and gear type
Catch Tables
Observers in the North Pacific Observer Program (Observer Program) collect biological samples and fishery-dependent information used to estimate total catch and interactions with protected species in the Bering Sea/Aleutian Islands and Gulf of Alaska. Managers use data collected by observers to manage groundfish and prohibited species catch within established limits and to document and reduce fishery interactions with protected resources. Scientists use observer data to assess fish stocks, to provide scientific information for fisheries and ecosystem research and fishing fleet behavior, to assess marine mammal interactions with fishing gear, and to assess fishing interactions with habitat. Each year, an Annual Deployment Plan (ADP) describes how observers and electronic monitoring (EM) will be assigned to vessels and processors in the upcoming year and an Annual Report provides information, analysis, and recommendations based on deployment of observers and EM by the Observer Program during the previous year.
The Annual Deployment Plans in the groundfish and halibut fisheries off Alaska do not deploy observers and EM into fisheries (because the fishery is not able to be identified before fishing occurs) but instead observers and EM are deployed to trips and vessels across all fisheries. There has been interest in comparing observer and EM coverage across the resulting fisheries, however, so summaries of catch by area and gear type have been included in Annual Reports for 2013 through 2017 (NMFS 2014-2016, Alaska Fisheries Science Center and Alaska Regional Office 2017, Alaska Fisheries Science Center and Alaska Regional Office 2018). The total catch of groundfish and halibut (retained and discarded) was summarized by area and gear type from the NMFS Catch Accounting System (CAS) and are available in the 2013 – 2019 Monitored Catch Tables (XLS). This allows for comparisons of the metric of catch weight derived from the CAS. Catch estimation methods used in the CAS are described in detail in Cahalan et al. 2014.
It is important to note that the proportion of catch weight monitored for a subset of fishing activity (i.e., a fishery) should not a priori be expected to equal the deployment rates (proportion of trips selected for coverage) specified in the ADP. In particular, if there are differences in fishing characteristics between the subsets of fishing activity, specifically differences in catch weights (or discard rates) per trip, those differences will be reflected in the relative proportions of catch monitored. For example, within the partial coverage trawl stratum, trips in the pollock fishery will have very different total catch weights and discard characteristics than trips in flatfish fisheries. In addition, there are several other factors that will contribute to the apparent inconsistencies between proportion of catch monitored, the proportion of trips monitored, and the deployment rate specified in the ADP. These include the actual number of trips selected (sample size), variability in deployment due to random chance, the ratio of number of trips in each of fisheries, and lack of independence between the coverage rates within a sampling stratum (more trips observed in one subpopulation (fishery) equates to fewer observed trips in the other subpopulations since all the trips across the different subpopulations must add to the total number of trips selected).
In these summaries, the catch of each species or species grouping is the sum of the amount of catch for that species or the species that comprise the species grouping, across all fisheries in an FMP area by a particular gear type and sector. Descriptions of the species within each of the species groupings can be found in the Appendices of previous Annual Reports (NMFS 2014- 2016). Catch identified as "Retained" indicates catch that was offloaded (minus dockside discard). Catch identified as "Discarded" indicates catch that was estimated as at-sea discard. “Observed Catch” is used for 2013 through 2017 and indicates catch that occurred on trips where an observer was present. Beginning in 2018, catch is identified as “Monitored” if an observer was present on the trip or some video was reviewed on the EM trip. The rationale for defining monitored trips this way for EM trips is that it is most similar to the way in which trips in other strata are considered observed (i.e., irrespective of whether or not haul information or usable species composition data were collected). “Total Catch” represents estimates of catch from all trips regardless of whether it was observed or monitored.
All catch and discard information, including halibut, is presented in round weight metric tons. If species were landed in a condition other than round weight then standard product recovery rates (PRRs) were used to obtain round weight. Halibut that were landed in ice and slime were additionally corrected using a standard 2% correction for ice and slime.
Halibut that are incidentally caught in federally managed groundfish trawl, hook-and-line, and pot fisheries are required by regulations to be discarded, regardless of whether the fish is living or dead. Halibut bycatch is tracked in the groundfish fisheries using prohibited species catch (PSC) limits. PSC limits are applied to specific target fisheries, gear types, and seasons. In the halibut IFQ fishery there is a length retention requirement of 32 inches below which fish must be discarded.
To increase the survival of incidentally caught halibut that are released, regulations require that halibut be returned to the sea following careful release methods. However, despite careful handling, some fish die from being caught and handled and the probability of morality depends on the target fishery and gear. For example, there is higher survival of discarded halibut caught with longline gear then that caught with trawl gear. The North Pacific Fishery Management Council uses viability (injury and condition) data collected by observers to generate halibut discard mortality rates (DMRs) in Alaskan groundfish fisheries. Halibut mortalities, the product of DMR and PSC, accumulate over the course of the season, and once the specified limit is reached for a given fishery, that fishery must be closed. For the in-season application of DMRs by management, DMRs are specified based on projections from historic DMR estimates. The International Pacific Halibut Commission (IPHC) also uses DMRs in halibut stock assessments, however they apply annual estimates of DMRs to account for past discard mortality. A DMR of 0.16 is used to estimate halibut discard mortality in the halibut fishery.
DMRs are not applied to raw observer data prior to expansion to the entire fishery, with the exception of halibut discarded under an ongoing Exempted Fishing Permit (BSAI trawl catcher-processors) allowing for sorting of halibut from the catch on-deck and prior to the catch being processed. Therefore, in order to present observed and unobserved catch, the data in these tables are presented without DMRs. As such, these data represent total catch - not total mortality; it is important to recognize that not all of the halibut that were discarded would have died.
Caution should be exercised when interpreting the results for halibut in the halibut IFQ fishery in these tables, however. For longline catch, the estimated weight of each species caught is the product of the estimated number of fish, the mean weight per fish, and the proportion of the catch that is discarded. While these methods provide unbiased estimates of total catch, the estimate of at-sea discards relies on the assumption that the proportion of the number of discarded is equal to the proportion of the weight discarded. The Pacific halibut fishery is the only federally managed groundfish fishery with a regulatory minimum size limit (32 inches). Because the minimum size limit requires smaller fish to be discarded, this assumption is not valid in the directed halibut fishery.
Starting in 2016, selection sampling methods for halibut were changed so that halibut selection was randomized within sampled hauls, making these data collections consistent with methods used in other fisheries and providing data that was used to assess the magnitude of bias associated with estimates of at-sea halibut discards in the directed fishery. These data were used to develop a model in late 2019 to convert the percent numbers discarded to percent weight discarded, and resolving the potential bias. These results were presented at the 2019 American Fisheries Society Meeting, and they suggest that the weight of halibut discarded on sampled hauls in the directed halibut fishery is overestimated by approximately 35%. This conversion method will be documented in a forthcoming NOAA Tech Memo and incorporated into the estimation process as soon as possible (expected in 2021).
References
- North Pacific Observer Program Annual Reports
- Cahalan, J., J. Mondragon, and J. Gasper. 2014. Catch Sampling and Estimation in the Federal Groundfish Fisheries off Alaska: 2015 Edition. NOAA Tech. Memo. NMFS-AFSC-286, 46 p.
- R Core Team (2017). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.
