Tag Archives: rockfish

Alejandro Frid: rockfish & predation risk theory

Vancouver Aquarium Marine Science Center

Focusing on quillback rockfish and interactions with one of their prey, 3 genera of demersal shrimp which show strong spatial association.  An example from 8 reefs in Howe Sound and adjacent Georgia Strait, depths 14-25m, daytime, 10 Jul – 18 Nov, 2008

Lingcod are the main predator of quillback rockfish.  Estimated biomass in Strait of Georgia down 90% in last 100 years, majority in Howe Sound are <75cm.  Smallest quillback should have strongest avoidance of encounters with lingcod at the expense of access to the shrimp.  Counts per minute (CPM) of small quillbacks rise with shrimp and fall with lingcod.  Large quillback CPM also rises with shrimp, but doesn’t alter with rising lingcod.

If we control for structural complexity of the habitat, then shrimp CPM decreases with rising activity of rockfish.

Predators should be managed not for demographic persistence alone, but for the maintenance of risk-driven ecological processes.

Eric Eisenhardt: Efficacy of bottomfish recovery zones

We have a great op in the San Juan Islands to compare marine reserves set up in ~1990 (mandatory) with bottomfish recovery zones (BRZ) were established ~7 years later (voluntary).  Overall, regulations have changed over time, essentially getting more restrictive.

Methods: 300 dives since 1997; transects to compare recovery zones with paired (nearby) reserve

lingcod length: bigger in reserves (2001-2002), but not significantly differnt in 06-07.  Same results with copper rockfish.

populations declining over this period 01-07, except black rockfish which have increased in population and size.

Why aren’t BRZs working better?

  • Using substrate maps, we can see that BRZs have similar areas to the the reference sites and actually have proportionally more rocky habitat.
  • Fishing effort is pretty even over all (e.g. along the west side of San Juan Island, Pile Point and Lime Kiln are about the same as Eagle Point)
  • Compliance issues may be the problem, or the size of the BRZs may be too small

It’s been 10 years.  What shall we do next?

  • Change nothing
  • One larger BRZ?
  • Make BRZs mandatory
  • Make them larger and mandatory