Winter Skate

Winter Skate Winter Skate

Winter skate (Leucoraja ocellata), also known as big or eyed skate, have only been reported in the Northwest Atlantic. Their range extends from the Gulf of St. Lawrence and the southern Newfoundland coast southward to Cape Hatteras. Within this range they have been reported from waters less than 1 m in depth to 371 m.

Status

On the eastern Scotian Shelf (NAFO Division 4VW) winter skate are found predominantly on the banks. Based on survey data, they are concentrated on Sable Island Bank and northward to Middle Bank, and on Banquereau Bank. They are caught in higher numbers in winter, concentrated along the southern side of Sable Island Bank and along the Stone Fence. Members of the fishing industry have reported that it is more difficult to catch skates in summer as they move onto the banks and spread out when the water temperature increases. In winter months, winter skate tend to be in deeper waters with a more concentrated distribution. There is little information on the distribution of winter skate in the inshore area of 4VW. Winter skate and little skate (Leucoraja erinacea), a closely related species, are sympatric over most of their range and are difficult to distinguish, especially at lengths less than 35 cm. Maximum length is reported to be about 109 cm, while little skate grow to a maximum length of about 53 cm.

The main source of information used to evaluate trends in the relative abundance of winter skate on the eastern Scotian Shelf was the July RV survey, which has been conducted since 1970. Additional information was obtained from an Industry skate survey conducted each spring since 1995. For analyses, skate were grouped into three size classes: (1) 75+ cm and longer, roughly corresponding to the adult portion of the population, (2) 60-74 cm, juvenile skate that are caught at a relatively high rate in the directed skate fishery, and (3) 36-59 cm, juveniles caught at a low rate in the directed skate fishery. Winter Skate below 36 cm in length were omitted from further analysis since they are difficult to distinguish from little skate. At the beginning of the July RV survey time series (1970s) juvenile winter skate abundance was low. Juvenile winter skate abundance increased during the 1970s, was fairly stable in the 1980s, and has been declining since the 1990s. Adult winter skate (75+ cm) abundance has declined since 1970. The catch rates indicate a decline rate of 90% over the 35-year time series. This decline appears to be ongoing.

Recovery Targets

Recovery targets have not been established for winter skate on the eastern Scotian Shelf. In this stock it is not possible to estimate either unfished biomass or MSY. Potential recovery targets could be the survey catch rates observed in the 1970s or the long term mean. As the average survey catch rate for adults in 2000-2004 is 16% of the average for 1970-1974, these proposed targets would be 3- 6 times the current catch rates.

Allowable Harm

Total mortality is estimated in the model and is apportioned between natural and fishing mortality. For the purpose of the model the fishing mortality is only attributed to catches that have been quantified. Model-based estimates of adult natural mortality may include unknown sources of human-induced mortality. For example, bycatch in the scallop and offshore clam fisheries is unquantified. At the current high rate of adult natural mortality, no recovery is expected even if reported directed and incidental catch is held to zero. There is little or no scope for human-induced mortality if this population is to recover and even then recovery is not certain. Because an increase in M of adults appears to contribute to the decline in abundance, removal of the aggregate human-induced mortality may not be sufficient to allow recovery. However a portion of the apparent increase in adult M may be due to unaccounted sources of humaninduced mortality (such as bycatch in the offshore scallop and clam fisheries). Skate egg cases occur on the bottom for 18-22 months hence are susceptible to bottom trawling, dredging, and other bottom disturbances. Although not a source of human-induced mortality, it should be noted that natural mortality of adults has increased over the same period that seal abundance has increased. This increase in adult natural mortality seems to be a contributing factor in the lack of recovery potential for this population. For more documentation regarding the winter skate click on the following links: CSAS Documents

SARA Public Registry