Elkhorn Slough Estuarine Research Reserve long-term crab monitoring database

The purpose of the long term crab monitoring program at Elkhorn Slough
Reserve, 1994-2024 was three-fold. First, we wanted to assess the
trajectories of the native crab populations, primarily the Oregon mud
crab, Hemigrapsus oregonensis, the Lined shore crab, Pachygrapsus
crassipes, and various cangrid crab species
(mostly Cancer antennarius and Cancer productus).
Secondly, we wanted to assess the population trajectory of the newly
invading (at the time) European green crab, Carcinus maenas.
Last, we wanted to optimize the probability of early detection of any new
invasive crab species at Elkhorn Slough. Secondarily, we recorded any fish
species, that went into the traps as by-catch. We used regular minnow
traps, minnow traps with an enlarged opening in one end, and Fukui fish
traps. All traps were baited (usually with anchovies), deployed at zero
tidal height (relative to mean low water) and soaked for 24 hours. Upon
retrieval, individuals were identified to species, and sexed and measured
(carapace width in mm) when possible. Trapping was conducted throughout
Elkhorn Slough over the years, but not all sites were trapped in all
years. The two most frequently trapped sites were Kirby Park and South
Marsh, which were trapped annually in fall. For analysis purposes, a
"set" of one small minnow, one large minnow, and one collapsible
trap should be used as one unit within one can calculate "crabs per
trap" whenever possible. Overall we have found for abundances of
native crabs that H. oregonensis is highest, followed by Cancer spp. and
then P. crassipes. It should be noted that P. crassipes does not
readily go into traps, so our population estimate of that species is most
likely a significant underestimate. We also found that abundance of the
invasive European green crab peaked in the early 2000s, then declined over
the next few years to have a smaller peak around 2011. Since then,
European green crab abundance has been declining. The most common fish
speices to appear in crab traps is Staghorn Sculpin.