In the past, sharks, skates and ray species have mainly occurred in incidental
fisheries. Now they are increasingly being directly targeted due to the depleted status
of traditionally targeted species. The life history characteristics of many
elasmobranch species make them more sensitive to high rates of fishing mortality.
The combination of these factors has resulted in the known local depletion of several
elasmobranch species; including the barndoor skate, Raja laevis, of the Northwest
Atlantic and the common skate, Raja batis, of Irish Sea. The longnose skate, Raja
rhina, occurs commonly as incidental catch in trawl fisheries off the coast of
California, Oregon and Washington. Commercial landings of skates, including R.
rhina, have increased dramatically along the U.S. West coast. The objectives of this
study have been to calculate accurate growth and maturity parameters for Raja rhina
in order that the vulnerability of this species to fishing mortality can be assessed. The
slow growth rates (k=0.04 to 0.06) and late ages-at-50% maturity (11 to 16 years
with maximum ages between 15 and 22 years, depending on sex and region) which
were calculated indicate that this species may be at great risk of depletion in the
future. Survey biomass trends indicate that R. rhina populations have remained stable
over the past twenty years. However, the possibility that biomass levels in the distant
past were much higher than they are at present cannot be ruled out. It is
recommended that the collection of fishery-dependent data for this species and other
skate species begins immediately. This information, along with the results found in
this are needed for a proper assessment for Raja rhina, so that the effects of current
fishing pressures can be evaluated and regulated appropriately. / Graduation date: 2006
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28596 |
| Date | 06 September 2005 |
| Creators | Thompson, Josie E. |
| Contributors | Heppell, Scott A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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