SaltyCajun.com - Spatial ecology of adult spotted seatrout

Read all 306 pages and this stuck out the MOST

Interestingly, Louisiana recently adopted (in 2006) a spatially-explicit management plan
for Calcasieu Lake. The premise of this management decision, which included a reduction in
daily bag limits and imposition of a slot limit, was to ‘preserve’ the renowned trophy-fishery for
spotted seatrout in Calcasieu Lake. However, the decision to enact this regulation was based
exclusively on socio-economic factors, rather than the biological status of the subpopulation. In
fact, no formal stock assessment was conducted as part of the decision-making process. Thus,
the status of the subpopulation (stock) was largely unknown (i.e., overfished or not?) at the time
regulations were changed. While perhaps setting a bad precedent for fisheries management (i.e.,
making a decision based purely on socioeconomic reasons), this situation affords a unique
opportunity to evaluate the response of spotted seatrout to a spatially-explicit (estuarine-scale)
regulations change (i.e., adaptive management, sensu Hilborn and Walters 1992). For example,
the response of the stock to the more stringent regulations could be examined by analyzing
fisheries independent monitoring data and conducting periodic, formal stock assessments (e.g.,
every five years). Obviously, response dynamics would largely depend on the status of the stock
when regulations were changed, which could be gleaned from the assessment. If the stock was
truly overfished at the time of the regulations change, response trajectories in the following
period might provide some indication as to whether the regulations were indeed stringent enough
to have a positive (re-building) effect. If no stock response is observed, this could indicate a
different type of management regulation (e.g., ‘input controls’ such as seasonal closures vs.
‘output controls’ such as bag limits) may be more effective. Finally, if the stock was considered
healthy at the time of the regulations change, subsequent abundance and biomass trajectories
could provide important clues to potential density-dependence processes in spotted seatrout. For

instance, an important question may be whether spotted seatrout are able to significantly increase

their abundance (when fishing pressure is relaxed) to a degree that allows them to exert higher
top-down predation pressure on other species in the ecosystem. As we move towards the future
in fisheries science and attempt to implement ecosystem-based fisheries management, questions
as these become important because seemingly conservative management actions for one species
(e.g., a reduction in fishing mortality) can often have unforeseen (negative) consequences on
other species within the ecosystem due to complex species and fisheries interactions (Pine et al.
2009).
This study demonstrated that adult spotted seatrout exhibit limited movements in coastal
Louisiana. The telemetry study provided strong evidence of high annual residency of adults
within an individual estuary (Calcasieu Lake), especially females (~90%). Furthermore,
conventional tagging data indicated large-scale movements in excess of 50 km were rare (< 2%),
albeit most tag recoveries occurred within two months post-release. Based on these results, I
hypothesized the spatial structure of spotted seatrout may best be represented as a
metapopulation comprised of subpopulations in each major estuary that were genetically similar
(primarily due to male straying), yet demographically independent due to seemingly low interestuarine
exchange rates (< 4%). Finally, I proposed an alternative stock assessment technique
(spatially-hierarchical models) that could be considered as a management tool to enhance and

promote the sustainability of Louisiana’s most sought after sportfish