National Shark Research Consortium
Pacific Shark Research Center - Moss Landing Marine Laboratories
Featured Projects
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NSRC Featured Project: Examining The Lives of Skates
Although most people are probably familiar with stingrays, many are unaware
of their cousin the skate. This bottom-dwelling, kite-shaped animal is
found throughout the world in temperate and polar regions, as well as in
deep waters of the tropics. More than 280 species of skate have been
discovered, making this family the largest of all rays. Unlike stingrays,
all skates give birth by laying distinctive, leathery egg cases. Skates are
closely related to sharks and rays, possessing skeletons made of cartilage
instead of bone; sharing this feature, these fishes comprise the
elasmobranchs.
Big skate, California skate, and longnose skate
Photo courtesy Moss Landing Marine Laboratories
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While skates have long been a targeted fishery and are a common component
of bycatch (fishes caught unintentionally and frequently discarded), very
little is known of the biology or abundance of most species thoughout their
range. However, fishing pressure has notably impacted the population
structure and distribution of skates, emphasizing the need for baseline
biological information of this poorly known group.
Trawling vessel. Photo courtesy NOAA
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Skates are fished with longlines, gillnets, and trawls along both coasts of
North America. Off the west coast, commonly occurring species include the
big skate (Raja binoculata), California skate (R. inornata), and the
longnose skate (R. rhina). The east coast is commonly represented by the
clearnose skate (R. eglanteria), barndoor skate (Dipturus laevis), little
skate (Leucoraja erinacea), winter skate (L. ocellata), and the thorny
skate (Amblyraja radiata). Only the large pectoral fins, or "wings" as
they are often referred to, are commercially marketed.
Since September of 2002, researchers from the Pacific Shark Research Center
(PSRC) at Moss Landing Marine Laboratories (MLML), under the auspices of
the National Shark Research Consortium (NSRC) and in cooperation with the
National Marine Fisheries Service (NMFS) Santa Cruz Laboratory (SCL), have
undertaken a study on central California skates to learn more about their
ecology, systematics, and life history. An increased understanding of
skates will help scientists advise government agencies, such as the
National Marine Fisheries Service, on commercial fishing policies related
to these species.
To conduct their research, scientists collected sharks, skates, and rays
each month from NMFS trawl surveys at five different depths, ranging from
59-1,778 ft (18-542 m) (Figure 1). Detailed biological assessments of all
skate and catshark specimens collected were performed by PSRC scientists at
Moss Landing Marine Laboratories. In an effort to reveal patterns of
distribution and abundance of these species, maps that indicate the
location of capture in relation to season, depth, bottom temperature, and
habitat type are also being created.
Figure 1. Trawl locations within Monterey Bay, CA
during September 2002 - March, 2003 surveys. Courtesy Joseph Bizzarro.
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Tonatiuh Trejo and Daniele Ardizzone dissecting a skate.
Photos courtesy PSRC.
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During a seven month period (September 2002-March 2003), a total of 2,639
chondrichthyans (sharks, skates, rays, and chimaeras), representing 15
species, was recorded from these surveys. Biological assessments consisted
of obtaining various measurements and weights as well as collecting
reproductive tracts, tissue samples, parasites, vertebrae for age and
growth estimation, and stomachs for feeding analyses. Initial assessment of
this information began in March 2003. The most abundant elasmobranchs taken
in the NMFS SCL groundfish surveys were the big (Raja binoculata),
California (R. inornata), and longnose (R. rhina) skates (Table 1).
Table 1. Catch of rays and skates retained from NMFS Santa Cruz Lab trawls for life history studies. Total # indicates the total number of specimens recorded during September, 2002 - March, 2003 surveys, % Total indicates the percent frequency of occurrence among the total chondrichthyan catch, and M:F represents the ratio of males to females recorded in the landings.
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The longnose skate dominated trawl landings and comprised 41% of the total
chondrichthyan catch. The largest longnose skate found in the catches
measured more than 3 ft in length (1090 mm). Although big skates nearly
4 ft in length (1357 mm) were collected, most in the area sampled were
found to be juveniles. Big and California skates were more common at
shallower depths than longnose skates (Figure 2).
Figure 2. Number of three skate species (big skate, California skate, and longnose skate) observed at different depths.
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PSRC scientists completed assessments of the reproductive biology for the
California skate, longnose skate, sandpaper skate (Bathyraja kincaidii),
brown catshark (Apristurus brunneus), and filetail catshark (Parmaturus
xaniurus). Results from this study will provide detailed information on the
life histories of skates and sharks commonly taken in commercial fisheries
for which little or no data are currently available. Research on this
project will continue, with emphasis placed on a new group of species over
the course of the next year.
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