RESULTS

METHODS AND ANALYSIS CONCEPTS

BACKGROUND:

The concept of this project follows typical habitat suitability analysis closely. Due to the pelagic stage of their development, Sebastes species exhibit type III suvivorship curve. The adults produce high number of eggs year after year in order to compensate the high juvenile and young-of-the-year mortality. Rockfish live in a very dynamic and unpredictable environment and this strategy is the result of best choices on the road of evolution. Studies have shown that high recruitment tend to be the result of a synergy of ocean upwelling, temperature, and food supply that materialize only once in many years. For instance, large number of bocaccio rockfish recruits survive only once in close to 20 years. This life history trait has proved to be successful for many ages, but it is deadly when faced with unrelenting fishing pressure. Human fishing efforts tend concentrate on the largest of any fish stock. Once the largest have been fished out, smaller and smaller individuals are gradually targeted because of the need to sustain fish landings. The collapse of Cod fisheries on the eastern seaboard is a classic example where apparently increasing landing turned out to be the result of much increased fishing efforts. There weren't more fish to be caught, it was just that humans were increasingly better at catching the remaining stock. This is usually signaled by apparent decrease in individual catch size and smaller catch per unit effort. The cod fisheries collapsed over a very short period of time as result. Rockfish population is under very similar kind of fishing pressure where large, mature fish with high fecundity are already fished out and more efforts are being concentrated on fewer and smaller individuals. Since rockfish often have very long recruitment period, and mature fish display highest fecundity, the increased fishing pressure is doubly bad news. The graph on the right side illustrate this point.

For those reasons explained above, protection of adult fish and more importantly, protection of young recruits become imperative. In order to have a successful recovery in rockfish population, it is best to designate marine protected areas that are off limits to fishery. Particularily, smaller and younger individuals that have just recruited need to be given a fishery free habitat to grow and attain to the kind of fecundity that is sustainable to the whole population. The habitat requirements of rockfish varies from species to species. However, many species primarily settle in subtidal areas where there are usually stratas and relief. Kelp and other vegetations, rock outcrop, low-lying cobbles and boulder fields are variously occupied by new recruits. Most species tend to settle at shallower depth until adulthood before returning to deeper regions as adults. In order to protect the young recruits, it is proposed that the protected areas stretch form just under tidal line and out to include those water column depths that is optimum to juvenile recruits. The analysis is geared toward the habitat requirements mentioned above.

ANALYSIS:

Analysis is done based on 3 criterias: Bottom Substrate, Biodiversity of the coastlines and Fragmentation of ocean floor.

The conceptual model of the analysis is here. For the substrate layer, the aim is to model a variable cost surface that will reflect different costs for a rockfish to travel across coastlines with variable bottom substrate. In turn, the anisotropic surface would reflect the "force" that pushes the rockfish into specific stretch of coastline. This simulation of "force" or "attraction" to rockfish is done with overlaying categorical values onto a surface of -1 value to simulate a change in Z values. When SURFACE module in IDRISI is executed on the overlaid surface, a slope surface between bottom value and various values can be calculated. These values are reclassified from categorical values of coastline substrate. Also, aspect values of these slopes are calculated by the module as well. Since aspect values are directions where a view is facing the steepest slope downward, it would mean the VARCOST surface having a force pushing away from the coastline. It is exactly what is NOT wanted since the analysis is attempting to model attraction of rockfish to the coastline, not away. To remedy this, the slope values are reclassified to be negative to make the aspect angles going inshore. When VARCOST is applied onto these two surfaces, the resulting variable cost layer reflects different attractive force that various coastline substratas exhibit to a rockfish toward shoreline. (varcost_friction.gnp) For the classification of substrate layer, please see here. A conceptual representation of varcost surface method is here

Rockfish are well documented to be in association with highly biodiverse habitats such as marine vegetation pathes. These patches not only provide refuge, there is also an abundance of food available. The calculation of biological layer takes this into account and produces a layer that reflects those coastlines with highest biodiversity. A ratio is calculated based on overall length of coastline with certain biological id (i.e. eelgrass_id) and the length of coastline that has eelgrass and also rock, gravel, rock/gravel/sand substrate. It is hoped that by including this ratio, there will be an association between biodiversity and the physical substrate factors that most often associate with rockfish habitat. A conceptual graph of biological factors is here

Fragmentation index of the Puget sound ocean floor is calculated in order to reflect the positive correlation between physical heterogeneity and habitat choice of young rockfish recruits. The fragmentation index follows the equation of (1-c)/(1-n) where c = number of cells that has different value in the specified matrix (5x5 in this case), and n = number of cell in the specified matrix (25 in this case). It is assumed that more heterogeneous ocean floor is more attractive to rockfish.

(http://www.whoi.edu/institutes/oli/currenttopics/ct_mpa_marine_reserves.htm Ocean Life Institution)