Prince E.D.,National Oceanic and Atmospheric Administration |
Luo J.,University of Miami |
Phillip Goodyear C.,1214 North Lakeshore Drive |
Hoolihan J.P.,National Oceanic and Atmospheric Administration |
And 5 more authors.
Fisheries Oceanography | Year: 2010
Oxygen minimum zones (OMZs) below near-surface optimums in the eastern tropical seas are among the largest contiguous areas of naturally occurring hypoxia in the world oceans, and are predicted to expand and shoal with global warming. In the eastern tropical Pacific (ETP), the surface mixed layer is defined by a shallow thermocline above a barrier of cold hypoxic water, where dissolved oxygen levels are ≤3.5 mL L-1. This thermocline (~25-50 m) constitutes a lower hypoxic habitat boundary for high oxygen demand tropical pelagic billfish and tunas (i.e., habitat compression). To evaluate similar oceanographic conditions found in the eastern tropical Atlantic (ETA), we compared vertical habitat use of 32 sailfish (Istiophorus platypterus) and 47 blue marlin (Makaira nigricans) monitored with pop-up satellite archival tags in the ETA and western North Atlantic (WNA). Both species spent significantly greater proportions of their time in near-surface waters when inside the ETA than when in the WNA. We contend that the near-surface density of billfish and tunas increases as a consequence of the ETA OMZ, therefore increasing their vulnerability to overexploitation by surface gears. Because the ETA OMZ encompasses nearly all Atlantic equatorial waters, the potential impacts of overexploitation are a concern. Considering the obvious differences in catchability inside and outside the compression zones, it seems essential to standardize these catch rates separately to minimize inaccuracies in stock assessments for these species. This is especially true in light of global warming, which will likely exacerbate future compression impacts. © 2010.
Goodyear C.P.,1214 North Lakeshore Drive
Transactions of the American Fisheries Society | Year: 2015
Abstract: Mean and maximum sizes in the catch are readily understood by both fishermen and scientists as important indicators of population health, but the maximum is more complicated to interpret because it increases with the number of observations. Size distributions of catches were computed for stable age distributions of hypothetical Atlantic populations of Blue Marlin Makaira nigricans. Fishing mortality rates were selected that reduced the population per age-1 recruit by 25, 50, 67, 75, and 90% by number from the unfished state. A new metric, NZ50, was applied to evaluate the performance of maximum size as an indicator of population status. Sample sizes required to include large marlin in a set of observations increased to disproportionately large numbers with increased fishing. With the best estimates of growth and a natural mortality of 0.1, the number of random observations required for a 50% probability of including a 350-cm individual increased by about 43% when the population was depressed by 25%. This value rose to more than 50-fold when the population was reduced below 10%. In contrast, mean lengths were reduced by only 1.6% to 14% and mean weights by 5% to 45% for the same range of fishing. These results provide quantitative evidence confirming the view that a diminished number of large fish is a sensitive indicator of excessive fishing, even when mean size of the catch shows only a small change. Increased catches above large size thresholds or nearing historical maxima could be sensitive indicators of stock recovery. Measures of the frequency of occurrence of individuals above some threshold defined for large fish will generally be superior to the maximuma observed in a sample (or set of samples) as a biological reference criterion because of the stochastic nature of individual observations. © 2015, C. Phillip Goodyear.
Goodyear C.P.,1214 North Lakeshore Drive
Fisheries Research | Year: 2016
Blue marlin (Makaira nigricans) are among many species of tunas and billfishes that require pelagic longline catch-effort statistics for stock assessments. Major controversies about stock status have arisen because of issues concerning habitat influences on catch rates, but models to describe how the species is distributed throughout its entire habitat are lacking. A habitat suitability model (HSM) of the size and spatial distribution of blue marlin habitat by month using habitat weighted-volume (H) is presented. It is estimated from oceanographic data partitioned by 1° of latitude and 1° of longitude in 50 layers from the surface to a depth of 1200 m using dissolved oxygen tolerances and temperature preferences compiled from electronic tagging. The physical habitat is an amorphous 3-dimensional space whose boundaries are constantly changing with seasonal and longer-term variations in climate. Fluctuations in habitat volume likely contribute to fluctuations in CPUE that are independent of population abundance and add unrecognized uncertainty to abundance indices used to estimate population benchmarks. The results highlight the need to expand stock assessments to include seasonal and annual climatology. The HSM-based habitat weighted volume model offers a way to validate analytical methods for using longline CPUE to monitor population health. © 2016 The Author
Hoolihan J.P.,University of Miami |
Luo J.,University of Miami |
Goodyear C.P.,1214 North Lakeshore Drive |
Orbesen E.S.,National Oceanic and Atmospheric Administration |
Prince E.D.,National Oceanic and Atmospheric Administration
Fisheries Oceanography | Year: 2011
Vertical habitat use of sailfish (Istiophorus platypterus) was evaluated using pop-up satellite archival tag data from the eastern tropical Atlantic, western North Atlantic, and eastern tropical Pacific. Data included Argos transmitted depth, temperature, and light level frequency histograms binned at 1-8-h intervals, and four recovered pop-up satellite archival tags that provided high resolution archival data recorded at 30-s intervals. We tabulated the proportions of time spent within each degree of water temperature relative to the surface temperature (Delta T) and proportions of time at temperature, as these are major input variables for habitat standardization models used in stock assessment procedures. Frequency distributions were calculated for daylight, darkness, and twilight for each of the three regions and for all regions combined. Vertical habitat envelopes indicated greater use of deeper strata in the western North Atlantic, compared to the hypoxia-based habitat compressed regions of the eastern Atlantic and Pacific. However, there were no significant differences in Delta T distributions when comparing the three regions, affirming this metric for its application in habitat standardization models. Published 2011. This article is a US Government work and is in the public domain in the USA.