Dynamic occupancy modeling of temperate marine fish in area-based closures

Area of Science:

• Marine Ecology
• Population Modeling
• Conservation Biology

Background:

• Species distribution models (SDMs) are widely used for marine species but often fail to account for detectability, leading to underestimated occupancy.
• Site occupancy models (SOMs) address this by modeling occupancy as a latent variable and incorporating detection submodels.
• Dynamic occupancy models (DOMs) are rarely applied to marine fish, and never for multiseason analyses.

Purpose of the Study:

• To develop and apply a multiseason dynamic occupancy model (DOM) for the cusk (Brosme brosme), a species of conservation concern.
• To incorporate detectability as a function of environmental variables, specifically current speed and algae cover, into the DOM.
• To compare model-estimated occupancy with direct observations to highlight the impact of detectability on occupancy estimates.

Main Methods:

• A dynamic occupancy model (DOM) was developed for cusk over a four-season period.
• A high-resolution 3D hydrodynamic model was used to estimate current speed.
• Seabed video surveys quantified algae cover, categorizing the study area into regions with and without canopy-forming algae.

Main Results:

• Modeled estimates of cusk site occupancy were significantly higher (0.88, 0.45, 0.74, 0.83) than those from video observations (0.57, 0.28, 0.43, 0.57) across seasons.
• Cusk detection probability varied with current speed and bottom type: higher detection with increased current in non-canopy areas, lower detection in canopy areas.
• Hydrodynamic modeling and habitat data improved occupancy estimates by accounting for detection probability.

Conclusions:

• Incorporating detectability into species distribution models is crucial for accurate marine species occupancy estimation.
• Dynamic occupancy models, utilizing environmental data like hydrodynamics, can correct for underestimation bias in traditional methods.
• This approach is vital for effective conservation and management of marine species, especially when using low-impact sampling methods.