Changes in Relative Occurrence of Cetaceans in the Southern California Bight: A Comparison of Recent Aerial Survey Results with Historical Data Sources

The Southern California Bight (SCB) is an interesting area of study due to the constant movement and migrations of marine mammals and especially cetaceans through these waters. The Southern California Bight is ecologically complex area that includes the Channel Islands and part of the Pacific Ocean. Cold water currents of the California Current flow south to meet the warmer waters of Southern California Countercurrent near Point Conception California. The SCB is characterized by warm and cold-water periods (May- October and November-April).

Systematic surveying marine mammals off of Southern California have been conducted since the mid-1970s. The data collected is useful because it offers abundance estimates of different species. The records of pre-1970s are mostly search and record information, which can still be beneficial for relative occurrence and abundance of marine mammals from 1950 to 1960s.

The research topic would be the changes in occurrence of Cetaceans over time. The research question (s) are what are the comparisons between literature reviews and 15 aerial surveys? What are the changes being seen between the search and record information from the 50s and 60s compared to the information from systematic surveys? The type of data used in this research was survey with annual information, meaning that the data is aggregate, interval or ratio data.

From the literature available, species rankings were collected and relative frequency of sightings from at-sea studies from 1950s to 2012 were analyzed. The results from 2008-2012 systematic aerial surveys were compared to eight other studies that best represented the relative occurrence of (SCB) cetaceans for specific time periods. Summaries of relative species rankings were places into tables. 16 species were observed during the most recent set of surveys. Multiple factors are discussed that would influence or bias the rankings, geographical location of the survey relative to species habitat, survey season relative to migration patterns, weather and sightability, observation platform, and historical species identification issues.

Overall, the articles was insightful is showing the ebbs and flows of relative occurrence of species throughout the Southern California Bight. What was not very clear was the movement from the literature to the species ranking. The process of creating these tables was not completely clear, other than that the abundance and sightings of different years has to do with the ranking and were different species are on the list. All information that was translated into the ranking list came from the systematic surveys and the other surveys from the 50s and 60s.

Smultea, M. and Jefferson, T. 2014. Changes in Relative Occurrence of Cetaceans in the Southern California Bight: A Comparison of Recent Aerial Survey Results with Historical Data Sources. Aquatic Mammals vol. 40 (1), 32-43.