Recent evidence suggests that overfishing of large predatory fishes has resulted in substantial population declines and pelagic longline (PLL) fishing is a major contributor. The primary objective of this dissertation is understanding factors that affect the interactions between marine fish PLL fishing. These factors are important to determine vulnerability of bycatch and target species, especially when PLL catch and effort data are used to estimate stock abundance. Chapter 1 reviews 107 publications/reports on this topic. Results indicate that accurate characterization of PLL gear performance requires empirical measurement of horizontal and vertical gear movement; and pop-up satellite tags (PSATs) are best suited for quantifying pelagic fish vertical habitat use if: (i) sampling resolution and data storage are not a function of tracking duration and (ii) substantial monitoring durations are employed. This review documents the current state of knowledge for these factors and guidance for future research. In Chapter 2, hook time-at-depth was monitored for commercial PLL sets targeting swordfish, Xiphias gladius. Temperature-depth recorders (TDRs) were deployed at the hook, systematically along the entire gear length. Results indicated that: (i) hook depth predictions based on catenary geometry drastically overestimated actual fishing depths and (ii) using catenary geometry fails to capture within- and among-set variability, potentially resulting in biased stock assessments. Chapter 3 used temperature-depth data from PSATs on swordfish and blue marlin (Makaira nigricans) and similar data from TDR monitored near-surface and deep PLL fishing to determine the diel probability of these species encountering PLL hooks. Results indicated that blue marlin and swordfish inhabit surface waters at night with similar probability of encountering PLL hooks but may have different vulnerabilities due to temporal separation in feeding with blue marlin preferring daytime and twilight and swordfish preferring nighttime. Therefore, reducing fishing during daylight hours may reduce blue marlin bycatch during PLL targeting swordfish. Chapter 4 alternated non-offset and 10° offset circle hooks during PLL fishing and compared the relative performance on catch rates, percent mortality, and deep hooking percentage. Results indicated that 10° offset circle hooks can reduce fishing efficiency and conservation benefits commonly associated with circle hooks.

The development and adaptation of gear technologies to local fisheries has been a management-oriented research strategy commonly used to mitigate the ecological effects of pelagic longline (PLL) gear on bycatch species. Grenada’s PLL fishery primarily targets yellowfin tuna, however while minimal, their bycatch of blue marlin and white marlin exceeds the Total Allowable Catch (TAC) allowed by the International Commission for the Conservation of Atlantic Tunas (ICCAT). A switch to circle hooks may benefit these nontargeted, bycatch species by reducing catch rates and haulback mortality, as well as increasing post-release survival. To determine differences in performance, assessments of 16/0 circle hooks and 9/0 J hooks were alternated over 26 sets between January and June 2018. Catch, mortality, hook location, length and grade of fish were compared between hook types. No differences in haulback mortality rate for all species, or yellowfin tuna grade were found between hook types. However, significantly fewer billfish collectively (t= 2.36, p= 0.028), and sailfish specifically (t= 3.04, p=0.005), were caught on circle hooks. Additionally, tuna caught with circle hooks had a 69% greater chance of external hooking compared to J hooks (X2 = 4.38 p=0.036). All other species analyzed had statistically similar catch rates regardless of hook type (p < 0.05), including, yellowfin tuna. The results of this study indicate the Grenadian PLL can reduce its impact on billfish bycatch by using 16/0 circle hooks without incurring negative effects on their tuna catch rate or grade. This research provides further evidence that circle hooks should be the recommended gear type when using a bycatch mitigation approach to manage PLL fisheries.

Submitted by (edna.saturno@ufrpe.br) on 2017-02-14T16:45:41Z No. of bitstreams: 1 Jose Carlos Pacheco dos Santos.pdf: 638792 bytes, checksum: 6f28321f4c3fd95cd1db01843c010e88 (MD5) / Made available in DSpace on 2017-02-14T16:45:41Z (GMT). No. of bitstreams: 1 Jose Carlos Pacheco dos Santos.pdf: 638792 bytes, checksum: 6f28321f4c3fd95cd1db01843c010e88 (MD5) Previous issue date: 2007-09-03 / Aiming compare the indices of catch per unit of effort, hook location, and the condition of the fishes caught in two different types of hook, the “circle” (18/0) and “J” (9/0), 81 pelagic longline sets in a equatorial area were observed. The indices of catches for the albacore (Thunnus alalunga), yellowfin tuna (Thunnus albacares) and swordfish (Xiphias gladius) had not presented a significant differences between the two the types of hook, whereas the bigeye tuna (Thunnus obesus) target specie in these fisheries, were significantly more caught in the circle hooks than in “J” hooks. The “circle” hooks also showed a mortality rate lesser than the “J” hooks, thus increasing the indices of non target species discarded alive, as for example the blue and white marlin, which in Brazil are being caught beyond the quotas stipulated by the ICCAT (International Commission for the Conservation of Atlantic Tunas). This fact brings a substantial quality improvement results during the disembark, resulting a high final products qualifying to export and consequently a best sale price. / No intuito de comparar o desempenho dos anzóis, o índice de captura por unidade de esforço, o posicionamento do anzol no corpo do animal capturado, e a condição do peixe no recolhimento, foram observados 81 lances de uma pescaria comercial com espinhel, operando no Atlântico sul equatorial, na qual os anzóis “circulares” (tamanho 18/0) e os anzóis do tipo “J” (tamanho 9/0) foram utilizados de forma alternada. As taxas de captura para albacora branca (Thunnus alalunga), albacora laje (Thunnus albacares) e o espadarte (Xiphias gladius) não apresentaram diferenças significativas entre os dois tipos de anzol, enquanto que a albacora bandolim (Thunnus obesus) principal alvo da pesca, foi significativamente mais capturada nos anzóis “circulares”, os quais apresentaram, também, uma taxa de mortalidade no momento do recolhimento muito menor, podendo assim aumentar a taxa de descarte vivo de animais que compõem a fauna acompanhante, como por exemplo os agulhões negro e branco, que no Brasil estão sendo capturados além das cotas estipuladas pela International Commission for the Conservation of Atlantic Tunas - ICCAT. Tal fato resulta em uma melhora substancial da qualidade do pescado na hora do desembarque, resultando, assim, em uma melhor qualificação do produto final para exportação e consequentemente um melhor preço de venda.