Evaluation of potential fishing location bias when an observer is aboard a Hawaii deep-set longline trip
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Evaluation of potential fishing location bias when an observer is aboard a Hawaii deep-set longline trip

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    The objective of the study discussed in this report was to evaluate if there is evidence that crews on deep-set longline vessels are less likely to fish within the U.S. Exclusive Economic Zone (EEZ) around Hawaii when a National Oceanic and Atmospheric Administration (NOAA) observer is aboard. There is particular concern about this behavior since the False Killer Whale Take Reduction Plan (FKWTRP) Final Rule went into effect on December 31, 2012 (77 FR71260). This technical memorandum and the results presented were completed in March 2018. Under the FKWTRP, NOAA Fisheries will close the Southern Exclusion Zone (SEZ) to deep-setting after the deep-set fishery reaches a “trigger” based on the false killer whale’s potential biological removal level. The FKWTRP defines the SEZ as bounded by 165°00′W longitude on the west, 154°30′W longitude on the east, the Papahānaumokuākea Marine National Monument and the main Hawaiian Islands Longline Fishing Prohibited Area on the north, and the U.S. Exclusive Economic Zone boundary on the south. The trigger is currently defined as two observed false killer whale interactions in the deep-set fishery that occurred within the EEZ around Hawaii and which NOAA Fisheries has determined are deaths or serious injuries. If the trigger is met, the SEZ will be closed to deep-setting for the rest of the calendar year and will be reopened at the beginning of the next calendar year. In the next calendar year, one of two things can happen: (1) if the trigger is not reached, the SEZ will remain open all year, or (2) if the trigger is reached, NOAA Fisheries will close the SEZ to deep-setting until certain bycatch reduction criteria have been met. This may mean the area is closed for longer than the calendar year. As this Final Rule may have created an incentive to avoid having false killer whale interactions observed inside Hawaii’s EEZ, there is concern that the crew is less apt to fish inside this EEZ when an observer is aboard. If this fishing location bias exists, it would violate the trigger’s underlying assumption that there is no location bias between observed and unobserved deep-set trips. To investigate the possibility of location bias, observer data recorded in the Longline Observer Data System (Pacific Islands Regional Office 2017), denoted as LODS, was used to estimate the deep-set longline (DSLL) fleet’s total number of operations inside and outside Hawaii’s EEZ for each calendar year from 2008 through 2016, where 2008–2012 were included to provide similar information for the 5-year period prior to the FKWTRP. These estimates are then compared to the total number of operations recorded in the Hawaii Longline Logbook Database (Pacific Islands Fisheries Science Center 2017), denoted as HLLD, that are inside and outside Hawaii’s EEZ. A statistical significant difference detected when comparing expanded observer with logbook values may indicate location bias. This comparison assumes that the definition of a fishing operation (set) and its recorded locations are equivalent between LODS and HLLD; that is, the instructions for recording the set’s locations are equivalent and recorded without error. A comparison of recorded locations from each dataset is provided in the next section. Additionally, this comparison considers HLLD as our finite population, and the two finite population parameters derived from HLLD that are being estimated are the (1) total number of operations inside Hawaii’s EEZ and (2) total number of operations outside Hawaii’s EEZ. LODS is viewed as a probability sample of HLLD; that is, the 2 values in LODS are used to estimate the totals, instead of HLLD sample values. If the values of the recorded locations between LODS and HLLD are not equivalent, then we have measurement error, one form of nonsampling error. Location bias is another form of nonsampling error that could be referred to as behavioral bias. Examining the validity of HLLD was not part of this analysis.
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