Observed and Monitored Catch Tables
Total catch of groundfish and halibut (retained and discarded) summarized by area and gear type.
Observed and Monitored Catch Tables
Observers in the North Pacific Observer Program (Observer Program) collect biological samples and fishery-dependent information used with industry reported fisheries data to estimate total catch (retained and discarded) 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), instead observers or EM are deployed to trips and vessels across all groundfish and halibut fisheries. However, there has been interest in comparing observer and EM coverage across resulting fisheries, 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 2013-2021 Observed & 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 proportion of trips within a sampling stratum that occur within a given fishery
- 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 within the sampling stratum)
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 groups 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. For 2018 onward, catch is identified as “Monitored” if an observer was present on the trip, some video was reviewed on a fixed gear EM trip, or salmon were observed for during monitoring of shoreside deliveries of a trawl EM trip. The rationale for defining monitored EM trips this way is that this definition 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 adjusted using a standard 2% correction.
Pacific halibut discard mortality rates
Halibut that are incidentally caught in federally managed groundfish trawl, hook-and-line, jig, and pot fisheries are required by regulations to be discarded, (unless participating in IFQ or CDQ halibut), regardless of whether the fish is living or dead. Halibut prohibited species catch is tracked in the groundfish fisheries against prohibited species catch (PSC) limits. PSC limits are applied to specific target fisheries, gear types, seasons, and management programs.
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 mortality 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 condition data (injury and viability assessments) 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 PSC limit, that fishery must be closed. For the in-season application of DMRs by management, DMRs are specified based on projections from historical 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 Exempted Fishing Permits (BSAI or GOA non-pollock trawl catcher-processors, 2015-2018) and the regulated deck sorting program (2019 onward), 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 halibut - not total mortality; it is important to recognize that not all of the halibut that were discarded would have died.
Discarded Pacific halibut in the IFQ fishery
For hook-and-line 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 catch, the estimate of at-sea discards relies on the assumption that the proportion of the number of discarded halibut is equal to the proportion of the weight discarded. The Pacific halibut fishery is the only federally managed fishery with a regulatory minimum size limit (32 inches) and this creates a unique data collection issue for observers who collect data from the unsorted (retained and discarded) catch without inferring which fish would be discarded by the vessel. As a result, the assumption that the proportion of halibut discarded by number equals the proportion discarded by weight is not valid and this results in over-estimates of halibut discard within the halibut directed fishery. To correct for this bias, NMFS has developed an analytic (modeled) method to adjust for this bias by adjusting the percentage of halibut retained to reflect the differences in mean weight per fish for retained (and discarded) halibut. In 2022, NMFS published a method to adjust for this bias by adjusting the percentage of halibut retained to reflect the differences in mean weight for retained (and discarded) halibut (Cahalan and Gasper 2022). Data in these tables beginning with 2021 reflect biased-corrected estimates of Pacific halibut discarded in the IFQ halibut fishery. Caution should be exercised when interpreting the results for halibut in the halibut IFQ fishery in these tables for the years prior to 2021.
- North Pacific Observer Program Annual Reports
- Cahalan, J., and J. Gasper. 2022. The commercial size limit for the Pacific halibut fishery off Alaska and its relationship to observer-derived estimates of at-sea discard. U. S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-432.
- 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.