Population/Cohort Studies of Target Species (1994-1998)
Changes in population structure of the target species should be
determined in conjunction with the broad-scale surveys, stratification
studies, source/retention/exchange studies, and frontal studies outlined
in previous sections. Such work should proceed during all years of the
study. These studies will provide baseline information on population
structure and rates of development, growth, fecundity, and mortality as
populations enter the bank and are transported around the gyre.
Questions: The population/cohort studies should address the following
Strategy: Locations and times of particular interest for the
population/cohort studies include:
- How do populations of target copepod species respond in terms of vital rates and changes in population structure as they are transported from source waters into the relatively eutrophic environment of the bank?
- What are the life history parameters (birth, development, growth, and death) of the target species populations during their drift around the bank?
Life history data can be obtained from analysis of net samples for
taxonomic, life stage, and age composition together with shipboard
measurements of growth and egg production rates, physiological state and
starvation. These measurements should be made in relation to key
physical variables which include temperature, stratification, advection,
mixing/turbulence, and time of day. Sampling should be done with high
enough spatial and temporal resolution to allow life history parameters
to be determined from the field data on population structure using
recently developed techniques in demographic analysis (Caswell and
Twombly, 1989). This will require very frequent sampling. Bearing in
mind that cruises at monthly intervals will produce samples that may not
be sufficient for such analysis, innovative approaches may be required
to complete this task.
- The inlet region of the bank north of the Great South Channel in January and February to examine changes in life history parameters of seed populations of Calanus and Pseudocalanus as they are carried onto the bank.
- The northeastern Bank in March to examine life history parameters of eggs and newly hatched cod and haddock larvae which are spawned in this region, as well as the copepod populations.
- The southeastern and southern flanks of the banks in April, May, and June to determine the life histories of cod and haddock mid-late larvae and pelagic juveniles as well as those of the Calanus and Pseudocalanus.