and found that there exist a significant overlap between the billfish resources and the exploitation activities targeting tunas and mahi mahi.

Transcription

1 Executive Summary Report 2016 Billfish Research in the Eastern Pacific Ocean Rosenstiel School of Marine and Atmospheric Science University of Miami January 2017 During 2016, the Eastern Pacific Ocean (EPO) Billfish Research Program of the University of Miami Rosenstiel School of Marine and Atmospheric Science (RSMAS) obtained comprehensive scientific insights into the spatial temporal population dynamics of sailfish, black marlin and blue marlin in the study area. The planned works were designed to provide scientific support to several ongoing billfish conservation efforts in the region, an activity that was intensely pursued by the program. Results were presented at meetings of the Central American Billfish Association (CABA) in Miami (Feb 2016) and in Guatemala (Oct 2016). In addition, Program scientists contributed four scientific conferences at the 6th International Billfish Symposium organized by the International Game Fish Association (IGFA) in Dania, Florida (Sep 2016). Analyses of our satellite tagging data demonstrated that contemporaneous habitat use by sailfish and blue marlin still matches very well the pre exploitation regional abundance distribution of the species in the 1970 s (Figs. 1 and 2). Spatial abundance was estimated from our stock assessment work making use of commercial fishery statistics collected in the 1970 s and provided to us by the Inter American Tropical Tuna Commission (IATTC). While sailfish are conspicuously associated with coastal ecosystems (Fig. 1), blue marlin appear to form three distinct and conspicuous hot spots in the Pacific Ocean. In the EPO, blue marlin distinctly concentrate in a region of the open ocean between Central America and Ecuador (Fig. 2). These new discoveries will help define units of stock, which are of fundamental importance to fishery management and policy development. Successful sailfish and blue marlin satellite tagging works resulted in one of the largest databases portraying sailfish and blue marlin migrations. The data provided unique opportunities of research and discovery on the species population dynamics relative to significant oceanographic characteristics, such as seasonal temperature regime changes found in the region (Fig. 3). The analyses on the temporal spatial dynamics of pelagic marine communities derived from satellite tagging in the EPO show that individual sailfish residence time coincides well with the spatial abundance of the sailfish caught as bycatch in the purse seine tuna fisheries (Fig.4). The high degree of association between density patterns of commercial catch and satellite tagged fish is indicative of strong population dynamic signals important for the definition of marine protected areas and other fishery policy and regulations necessary to protect the billfish resources. For example, the spatial time residency of sailfish and blue marlin were assessed relative to the marine protected areas designed and adopted by the Costa Rica Government to protect tuna species from fishery actions by the international purse seine fleets in the Costarrican Economic Exclusive Zone (EEZ)(Figs. 5 and 6). Such areas do not appear to fully protect the two billfish species from purse seining in the EEZ and support existing arguments that the Tico Tuna campaign may result in increased bycatch mortality of the billfish in hook and line fisheries within the Costa Rica EEZ. Furthermore, the researchers analyzed the extent of sailfish habitat use relative to the fishing intensity (fishing effort per unit of area) of coastal longliners (Fig. 7) 1

2 and found that there exist a significant overlap between the billfish resources and the exploitation activities targeting tunas and mahi mahi. Such overlap is in great part responsible for the high commercial fishing morality rates imposed on billfish in the region. The Program also analyzed four decades of sailfish, blue marlin, and black marlin population abundance distribution in the EPO using information provided by the IATTC (Figs. 8, 9 and 10). It was concluded that significant abundance depletion due to over exploitation has occurred in all three species and better protection of the charismatic billfish species is badly needed. Localized high billfish population densities are reflected by high catch rates observed in the recreational fisheries in Central America and Panama; however, such catch rates are due to habitat compression of the depleted populations as well as regional environmental changes favoring distribution, not increased abundance of the species. The use of Fish Attracting Devices (FADs) in Costa Rica has also increased the catch rates of blue marlin, but again this is thought to be an artifact associated with increased fishing power brought about by the use of FADs in offshore areas coinciding with areas of increased blue marlin residency (Fig. 6) and not related to an increase in regional billfish population abundance. The research works also put special emphasis on addressing sailfish daily behavioral aspects that are of interest to the recreational fishing sector. Program scientists used sophisticated satellite tags equipped with an accelerometer to measure sailfish hourly activity. A total of 960 fish hours were observed and the data analyzed show that sailfish activities are exclusively driven by light hours (Fig. 11), while animals are almost completely inactive and very close to the surface (upper 8 meters) during night hours. Interestingly, only during the full moon, sailfish were found to become slightly more active at night where they are utilizing the limited amount of increased moonlight (Fig. 11). Recreational hourly fishing statistics collected by boat in a Flor de Caña billfish tournament in Nicaragua in 2015 and fishery statistics by boat and hour in the for hire recreational fleet in Guatemala (Fig. 12) generated information necessary to explain the correspondence between diurnal sailfish activity patterns, mostly associated with feeding activities, and the expected daily catch cycles in the recreational fisheries. Satellite tag data also allowed researchers to express the differential depth distributions of sailfish in the region (Fig. 13). Diving behavior is not only driven by differences in daily light penetration in the sea that facilitates location of prey by the billfish, but also by habitat compression due to regional differentials resulting from the surfacing of minimum dissolved oxygen from deeper more anoxic waters. A minimum 1 ml of dissolved oxygen per liter of seawater is necessary for the survival of the billfish prey as well as billfish as predators, and such a limit is well correlated in the vertical habitat use of the sailfish (Figs. 11 and 13). In general, research activities in 2016 were completed according to planned works and they form a well integrated ecosystem wide view of the billfish population dynamics. This information will significantly contribute to the emerging institutions responsible for national and regional billfish conservation and management. The results presented in this summary were funded with donations of conservation minded persons. The RSMAS Billfish Research Program owes gratitude for the funding and in kind support received during this time otherwise none of these results would be available. 2

3 Scientists responsible for this report are Dr. Nelson Ehrhardt (Program Director), Dr. Mark Fitchett, and PhD Candidates Bruce Pohlot and Julie Brown. Figure 1. Sailfish abundance distribution in the Eastern Pacific and satellite tag tracks indicating habitat use. There is a high degree of association between historic spatial abundance and the habitat use descriptors developed from the tags. This is a matchingof similar biological processes occurring in the population dynamics of the sailfish expressed by two very different datasets. Sailfish is the most coastal of the billfish species when compared with blue marlin (Fig. 2). 3

4 Figure 2. Blue marlin abundance distribution in the Pacific during the 1970s and satellite tag tracks indicating habitat use. There is a high correlation between historic spatial abundance and the habitat use descriptors developed from the tags in three regions of the Pacific: Hawaii (IGFA data), Tahiti (IGFA data) and Eastern Pacific (Our project data). This is a matching of similar biological processes occurring in the population dynamics of the blue marlin but explained by two different sources of information and analyses. 4

5 Figure 3. Sailfish satellite tagging off Central America is one of the most intensive and with the highest tag density information available for the species anywhere in the world. Patterns of migration in the areas between upwelling regions (marked yellow green) are identified with food searching. Patterns of migration in the upwelling regions (marked magenta blue) are indicative of fast migrations through those areas, which are characterized by low levels of dissolved oxygen. 5

6 Figure 4. Upper figure. Areas most visited by the satellite tagged sailfish off the coast of Central America and Panama. Lower figure. 10 Year average spatial distribution of sailfish catch rate levels obtained in the tuna purse seine fleet in the eastern Pacific. There is a high correlation of the main areas where sailfish form larger concentrations. This information corroborates from two very different data sets that boundaries of the sailfish population in the region are well defined with preferences in areas at the boundaries of major oceanographic features that dominate the marine ecosystem in the region. 6

7 Figure 5. Sailfish most frequented areas off Nicaragua, Costa Rica and Panama obtained from satellite tagged fish and the tuna reserved areas established in Costa Rica to avoid international purse seine fishing in those areas. The sailfish distributions are not effectively protected from such fisheries (excepting in zone C) while the species is fully exposed to potential hook and line fishery developments in Costa Rica. Zones A and B established to protect coastal areas from commercial fishing create a refuge for sailfish in those zones but main habitat preference by sailfish are in areas not designed to protect the resource from longlining or any other hook and line gear that may be used to catch the so called Tico Tuna and mahi in the Costa Rican EEZ. 7

8 Figure6. Data from satellite tagged bluemarlin indicate that the species mostly frequented areas off Nicaragua, Costa Rica and Panama. The purse seine tuna reserved areas established in Costa Rica largely protect the blue marlin from such fisheries but fully expose the blue marlin populations to longlining and potential new hook and line developments targeting tunas and mahi in Costa Rica. Zones A and B established to protect coastal areas from commercial fishing create very limited refuge for blue marlin in those inshore zones. 8

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13 Figure 11. Sailfish daily behavioral patterns measured with satellite tags equipped with accelerometers indicate that sailfish activity measured by the tags is stricktly bounded by daily light hours (Upper left figure). Sailfish excibit a well defined diving pattern corresponding to hours of the day (Upper right figure). Depth of diving activities is conspicuously limited to about 55 meters due to low levels of dissolved oxygen at deepr layers of the ocean. Light penetration in the sea can reach up to 200 metters in this region; however, sailfish does not use the full extent of the iluminated habitat due to the compression from below of oxygen deprived upwelled waters. Sailfish activity is well correlated with diving activities (Lower figure), all which are identified with feeding behavior. 13

14 Recreational Fishing and Sailfish Activity Rhythms Figure 12. Hourly sailfish catch rates at the Flor de Caña tournament in Nicaragua in 2015 and sailfish hourly catch rates in the for hire recreational billfish fishing fleets in Guatemala coincide with daily fishing patterns as well as with the activity patterns defined from sailfish satellite tags. Sailfish remain active in excess of 2 hours relative to catch rates. This behavior may be a response of food satiation that may lower the effectiveness of baits and lures to capture billfish. Differences found after 15 hours local time are still subject of research. 14

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