Detecting Potential Population Trends in Non-Commercial Northeast Species

Direct overfishing is not the only concern of global fisheries.  Bycatch, habitat loss, food web alterations, and shifts in diversity and community composition are all potentially indirect effects on populations of both target and non-target species.  The status of non-commercial species is largely unknown as management focus remains on linking changes in community and ecosystem disturbances to fluctuations in commercial populations for which sufficient data exists.  The National Marine Fisheries Service Northeast groundfish bottom-trawl survey datasets were analyzed to address potential population fluctuations in commonly-encountered non-commercial species.  A power analysis using data from the fall time-series (1963-2006) was conducted to determine the ability to identify significant declining trends within the next 10 or 15 years.  Potential declining trends were chosen from IUCN A1 criteria stating that a 30%, 50%, or 70% decline over the longer of 10 years or 3 generations is sufficient to label a species as vulnerable, endangered, or critically endangered, respectively.  Results indicated an overall low power for most species, and a strong divergence between unassessed and assessed species with much greater percentages of assessed species exhibiting a power greater than 0.6.  The low power was caused by the high variance in the time-series trend for many species, and indicates that the survey trends cannot be confidently used alone as indicators of population status.  However, some species were in a current period of significant decline, as identified by a breakpoint and correlation analysis, and thus, still likely require management attention.   Additionally, alternative methods to gather data on these species or surveying on a finer spatial and temporal scale may shed more light on population fluctuations within unassessed species and will contribute greatly to successful implementation of ecosystem-based fishery management.