An Initial Analysis Of Alternative Sample Designs For The Deployment Of Observers In Alaska PDF Download

Changes in regulation enacted in 2013 have enabled the Alaska Fisheries Science Center's Fishery Monitoring and Analysis Division (FMA) and the Alaska Regional Office's Sustainable Fisheries Division to work collaboratively on an Annual Deployment Plan (ADP). Each ADP documents how the National Marine Fisheries Service (NMFS) plans to deploy observers into fishing activities for the coming year under the limits of available funding. Draft ADPs are presented to the North Pacific Fishery Management Council (Council) during September - October and are finalized in December. The sampling design for observer deployment has two elements: how the population is subdivided (i.e., stratification schemes) and how available samples are allocated (i.e., allocation strategies). Here the relative performance of 10 alternative sampling designs (at the primary sampling unit- the trip) are compared in support of the draft 2018 ADP. These alternative sampling designs consisted of the combination of two stratification schemes (gear-type only or gear-type × tendering activity), two metrics upon which to base optimizations [one consisting of discard of groundfish with Prohibited Species Catch (PSC) of Pacific halibut and the other consisting of the prior and PSC of Chinook salmon], and three allocation strategies (no optimization, a "hurdle" approach to optimization, and a optimization only). All optimization allocations incorporate three variables measured over the past 3 years: variance in the metric, the average cost of observing a trip, and the number of trips. Total afforded sample size is determined by the available budget and the average cost of observing each trip. Resulting selection rates derive from sample size, allocation weightings and the anticipated fishing effort which was defined as the most recent complete year of data. The total number of observer days that can be afforded is 4,062 which represents a 33% increase from 2017. Gap analyses that examine the chance of at least one or three observed trips in a NMFS Area × gear type combination (cell) were used as a performance metric. Gap analyses illustrated that stratifications based on gear type (3 strata) were outperformed by stratifications based on gear type × tendering activity (6 strata). Potential gaps in observer coverage appear to be mostly concentrated in areas with low fishing effort with fewer than 12 trips in a cell. Simulations were performed to measure the potential impact of unknown vessel participation in electronic monitoring (EM). The variability in gap analyses from randomized differences in EM participant vessels was relatively minor (less than 10% probability of observation shifts across deployment designs). The NMFS recommended an observer deployment design for the draft 2018 ADP that has gear type × tendering stratification and uses a "hurdle" approach to sample allocation wherein 15% base coverage is obtained first across all strata and the remainder is optimized according to the variance in the metric of discarded groundfish catch combined with PSC Pacific halibut and Chinook salmon. At their October 2017 meeting the Council did not support the NMFS recommendation and instead proposed a five strata design with optimal sample allocations based on discarded groundfish catch and PSC of Pacific halibut only. Comparisons between the NMFS and Council recommended designs were included in the final 2018 ADP. [doi:10.7289/V5/TM-AFSC-364 (https://doi.org/10.7289/V5/TM-AFSC-364)]