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(Illex Illecebrosus) and Preliminary Annual Landings-Per-Unit-Of-Effort for the Southern (USA) Stock Component

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(Illex Illecebrosus) and Preliminary Annual Landings-Per-Unit-Of-Effort for the Southern (USA) Stock Component Working Paper Not to be cited without author’s permission Characterization of Body Weight Data from the Landings of Northern Shortfin Squid (Illex illecebrosus) and Preliminary Annual Landings-per-Unit-of-Effort for the Southern (USA) Stock Component by Lisa Hendrickson and Alicia Miller Northeast Fisheries Science Center April 20, 2020 Background Similar to other ommastrephid squid species, the Northern shortfin squid (Illex illecebrosus) stock, hereafter referred to as Illex, is a transboundary resource. Illex fisheries occur within the Exclusive Economic Zones (EEZs) of the USA and Canada, as well as in international waters that are managed by the Northwest Atlantic Fisheries Organization (NAFO). Thus, the northern stock component (NAFO Subareas 3+4) is managed by Canada and NAFO and the southern stock component is managed in the USA (NAFO Subareas 5+6) by the Mid-Atlantic Fishery Management Council (MAFMC; Hendrickson and Showell, 2019). The resource constitutes a unit stock throughout its range in the Northwest Atlantic Ocean (Hendrickson 2004). The only documented spawning grounds for the species is located in US waters on the continental shelf and upper slope in the Mid-Atlantic Bight (Hendrickson, 2004). The small-mesh bottom trawl fishery for Illex occurs on the spawning grounds (Hendrickson and Hart 2006). The fishery occurs when squid are available in commercial quantities, primarily during June-October, near the edge of the US shelf (Hendrickson and Holmes 2004; Hendrickson 2004). The application of most conventional stock assessment methods are inappropriate for I. illecebrosus and other cephalopod species given their unique life histories and population dynamics (Hendrickson 2004; Arkhipkin et al. 2015; Arkhipkin et al. In Press). Like other ommastrephids, I. illecebrosus is semelparous and spawns throughout the year with several peaks that result in the presence of multiple, overlapping sub-annual cohorts. The species has a lifespan of less than one year (Dawe and Beck 1997; Hendrickson 2004). Illex stock assessments are data-poor because the existing Northeast Regional fishery-dependent datasets are not collected at the high temporal and spatial resolution (i.e., daily, tow-based catch, effort, fishing location and biological data) required to apply the in-season depletion-type models that are used for other ommastrephid squid stocks (NEFSC 1999; Arkhipkin et al. 2015; Arkhipkin et al. In Press). The existing fishery data requires merging of the Dealer and Vessel Trip Report Databases to obtain trips that are a 1:1 match. Trips that are not matched do not contain the data needed for catch-per-unit-of-effort (CPUE) analyses. In addition, the spatial (large Statistical Areas for reporting fishing locations primarily resulting in a single location per Illex trip) and temporal (average tow duration and number of tows by subtrip) resolution of these data is inadequate for accurate in-season stock assessment. Another requirement for in-season assessment 1 Working Paper Not to be cited without author’s permission is a pre-fishery Illex survey (NEFSC 1999) conducted with commercial fishing gear similar to the survey conducted in 2000 (Hendrickson 2004). The spring and fall NEFSC bottom trawl surveys are conducted during periods of the species’ annual migration on (spring survey) and off (fall survey) the continental shelf. CVs for the spring survey indices are higher than they are for the fall survey indices. Consequently, estimates of Illex relative abundance and biomass on the US shelf are derived using the fall rather than the spring survey data (NEFSC 1999). History of Illex illecebrosus in-season stock assessment The 2017-2019 Illex fishery closures led to the MAFMC’s Science and Statistical Committee (SSC) to revisit the potential for implementation of in-season assessment of the US stock component. Given this objective, it is important to understand what has already been accomplished on this topic to avoid repetitive research. Since 1996 (Hendrickson et al. 1996), NEFSC assessments of I. illecebrosus have recommended conducting real-time or in-season stock assessments that can be used for adaptive, in-season management. Following a 1998 fishery closure, the Illex fishing industry requested implementation of an in-season management program in order to avoid foregone yield during years of high on-shelf abundance. Conversely, there must also be the recognition of potential fishery closures during periods of low Illex abundance, which emphasizes the need for a pre-fishery survey, conducted by an Illex fishing vessel, the data from which can be used to derive an initial abundance estimate. In order to evaluate the feasibility of conducting in-season Illex assessments, beginning in 1999 I obtained multiple research grants that allowed me to conduct several pilot studies on this topic. Prior to 1999, I also began collecting body weight data from Illex processors. The history of collaborative research conducted to collect the high-resolution CPUE and biological data required for in-season stock assessment such as a weekly, depletion model are summarized in Table 1. Although these projects demonstrated that in-season data collection and assessments were possible, previous fishery managers were not in favor of adopting it because it would require a different type of infrastructure than currently exists. Furthermore, the required data for such assessments was (and still is) lacking and would be more costly to collect. For example, an e-VTR tow-based data collection framework with daily reporting and in-season assessment analysis would be necessary. The current management framework is also not set-up for adaptive fishery management. Real-time or in-season assessment of stock size was recommended in previous assessments to ensure adequate spawner escapement for each sub-annual cohort that is fished in order to increase the probability that subsequent recruitment is adequate to sustain each cohort. In- season assessment has been implemented in other ommastrephid stocks to reduce the likelihood of foregone yield during high abundance years and recruitment overfishing during low abundance years (Basson et al. 1996; Arkhipkin et al. In Press). Previous Illex assessments incorporated data collected from a research project designed to demonstrate the feasibility of real-time at-sea collection of tow-based fishery and body weight data. During 1998-2003, tow-based fishery data were reported daily by Illex fishermen to the NEFSC via Boatracs macros and a captain-specific password-protected e-VTR website. The at- sea data were automatically uploaded to the NEFSC e-VTR website and combined with the remainder of the required VTR data fields (Hendrickson et al. 2003). Another grant-funded research project involved a pre-fishery, pilot Illex bottom trawl survey using two chartered Illex 2 Working Paper Not to be cited without author’s permission fishing vessels (Hendrickson 2004; NEFSC 1999; Hendrickson and Hart 2006). Data from these research projects were then incorporated in the 1999, 2003 and 2006 stock assessments to demonstrate their utility for in-season weekly estimates of stock size using depletion models. This Working Paper focuses solely on the southern component of the Illex stock with the objective of extending the time-series of landings-per-unit-of-effort (LPUE) and body weight data that have been evaluated in previous Illex stock assessments through 2004. An Illex stock assessment has not been conducted since 2005 due to the lack of adequate data at the resolution required to conduct in-season depletion modeling and to estimate %MSP Biological Reference Points (NEFSC 2006). Data from 15 additional fishing seasons, from 2005-2019, are evaluated here in addition to the 1997-2004 data that were previously evaluated. Characterization of data from these additional fishing seasons will allow for the comparison of body weight and LPUE trends during a broader range of low, medium and high periods of Illex abundance on the U.S. shelf for the purpose of evaluating the potential for these data to be used to conduct in-season stock assessments. Methods Mean Body Weight Mean body weight has been used as a measure of productivity for the Illex stock in previous stock assessments (NEFSC 1999; NEFSC 2003; NEFSC 2006; Hendrickson et al. 2001). This report characterizes both annual and weekly Illex body weight data collected from the landings during 1997-2019. The body weight data for 1997-2003 was collected as part of a cooperative research study that involved real-time, fishery-dependent data collection. I continued collecting these data in order to generate a time-series of high-frequency body weight data with which to evaluate changes in stock productivity. Body weight data for 2004-2006 and 2009-2018 were collected from landings of the directed fishery by QA/QC staffs from the two primary Illex processors. Data were generously provided by Lunds Fisheries in Excel spreadsheets which required some reformatting, for 2016-2019. Data were also provided by Seafreeze Ltd. on their QA/QC sampling forms and required extensive keypunching by staffs from the Population Dynamics Branch. Seafreeze Ltd. provided us with additional information to identify each trip and this allowed me to add “date landed” from the Dealer Database to their dataset in order to assign week of the year to the samples from each trip. Mean body weight for the samples collected by port samplers was computed by dividing the sample weight by the number of lengths in the sample. Samples collected by port samplers included 100 squid per market category. These samples were obtained opportunistically with the objective of collecting the numbers of monthly samples that I requested by market category, fishery region and year. Such samples do not include all market categories from each trip, unlike the Lunds Fisheries and Seafreeze Ltd. samples. As a result of the different sampling protocols, the two mean body weight datasets were summarized separately. For the purpose of comparing trends, stratified mean body weights for the NEFSC fall bottom trawl surveys (Hendrickson and Showell 2019) are also presented.
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