Growth and maturity of Longnose Skates (Raja rhina) along the North American West Coast

Abstract

Information on the growth and maturation of exploited fishes is important for assessing and managing fish populations. These life history processes commonly vary spatially and temporarily in marine fishes due to environmental and ecological factors, which can have implications for management. However, acquiring biological information on marine fishes on large spatial and temporal scales can be expensive and time consuming. This is especially true for elasmobranchs because elasmobranchs do not possess otoliths, which are commonly used for age-estimation in teleost fishes. Instead, alternative methods are used which are time intensive and often have reduced precision. The Longnose Skate is a species of elasmobranch commonly caught as bycatch in groundfish fisheries along the North American West Coast. Individuals are acted upon by variable environmental and ecological conditions along their large range that may impact growth and maturity. The first chapter of this thesis explores spatial variability in the size-at-age and size-at-maturation of Longnose Skates along their geographic range from the Gulf of Alaska to Southern California. We found that growth and maturity varied between the regions (1) Western and Central Gulf of Alaska, (2) Eastern Gulf of Alaska/ British Columbia, and (3) the U.S. West Coast along a latitudinal cline. The second chapter explores the application of an emerging technology called Fourier transform near infrared spectroscopy (FT-NIRS) to more rapidly estimate ages for Longnose Skates. We found that FT-NIRS technology was able to predict Longnose Skate ages within 1.45 years of the traditionally generated age 68% of the time (R2 = 0.87, RMSE = 1.45 years) in approximately 1/8th of the time. These findings suggest that life history parameters used in stock assessments, such as size-at-age and maturation-at-size, do vary spatially. Additionally, efficiencies can be gained by utilizing FT-NIRS technology to estimate ages for Longnose Skates which may make it possible to increase the quantity and temporal resolution of age data that is incorporated into stock assessments.