Estimation Of Instantaneous Rate Research Articles

Estimates of exploitation rates of the spiny lobster fishery for Panulirus argus from tagging within the Bahía Espíritu Santo ‘Sian Ka'an’ Biosphere Reserve, Mexican Caribbean

The Caribbean spiny lobster (Panulirus argus) fishery is currently being assessed for a certification process. It is the main economic activity within the Biosphere Reserve of Sian Ka'an-Mexico (SK), which is a marine-protected area where restricted access fishing is allowed. In this study, commercial catch rates were examined, and lobsters over a wide size range were tagged throughout the 2010/2011 fishing season, to assess fishing mortality rates and movement patterns in Bahía Espíritu Santo-SK. Lobster tag recovery data were aggregated into 2-week periods and analysed using a modified Brownie model that was parameterized to account for lobster tag-reporting, and the lobster tag-retention rates. This allowed the estimation of instantaneous rates of natural and fishing mortality, considering catchability and fishing effort. Independent aquaria trials were conducted to better estimate lobster tag retention, tagging-induced mortality and interviews with fishermen were conducted to better estimate lobster tag reporting. Based mainly on legal-sized juveniles with fast growth rates found in casitas, the stock is subject to fishing to a maximum depth of 20 m, because of the prohibition of SCUBA diving and the use of other fishing gear. The Brownie model indicated that exploitation rates within this bay area were high,>0.94. Changes in catch per unit of effort and catchability throughout the season explain how the ‘casita/campo’ system allows for a seasonal replenishment of juveniles and adults, which has kept the landings relatively stable for the past decade.

Loss of tags, double-tagging and release methods for eastern king prawns, Penaeus plebejus (HESS): laboratory and field experiments

Experiments were done in the laboratory and in the wild to determine the best procedure for tagging eastern king prawns in estuaries in New South Wales, Australia. At the end of an 88-day experiment in the laboratory, there were no significant differences in mortality among prawns tagged with wide (2 mm wide) or narrow (1.5 mm wide) streamer tags, and untagged (control) prawns. Loss of tags was far greater for narrow (70%) than wide (38%) tags because of greater shedding of tags (38 and 2%, respectively). Mean mortality of untagged prawns at the end of the experiment was 13%. Estimates of instantaneous rates (week −1) of tag-induced mortality and shedding of tags combined were derived using an exponential decay model were 0.056 (± 0.01) and 0.039 (± 0.014) for narrow and wide tags, respectively. The instantaneous rate of mortality for untagged prawns was 0.011 (± 0.008) week −1. Growth of prawns that survived to the end of the experiment was unaffected by tagging or the size of the tag. Survival of tagged prawns in the wild did not differ between those released on the surface or bottom, nor between prawns released one or two nights before harvesting. It also did not differ between single- and double-tagged prawns. No double-tagged prawns shed tags. This pattern was the same as that for single-tagged prawns in the laboratory experiment. Streamer tags 42 mm long and 2 mm wide should be used to tag eastern king prawns longer than 20 mm C.L. (carapace length). In waters no deeper than 7 m, tagged prawns can be released on the surface and exposed to harvesting as early as one night after being released. It is also recommended that double-tagging be considered as a viable method for investigating mortality and shedding of tags among penaeids.