Laguna San Ignacio Ecosystem Science Program (LSIESP) Preliminary Field Report – 2009
The Laguna San Ignacio Ecosystem Science Program (LSIESP) began the 2009 winter season with the arrival of the gray whale research Team at the lagoon on 17 January. The 2009 gray whale Team is led by Steven Swartz (CRA), Jorge Urbán (UABCS), and Alejandro Gómez Guallardo U. (UABCS) and includes five researchers and graduate students from universities in Mexico: Sergio Martínez (UABCS), Hiram Nanduca (UNAM), Anaid Lopez Urbán (UNAM), Ana Liria Del Monte Madrigal (UABCS), Maurico Nájara Caballero (CICIMAR), and Héctor Pérez Puig (CICESE). The Team will remained at the lagoon until the end of the 2009 gray whale winter season in early April.
Gray whale monitoring and assessment
The two primary activities are conducting weekly census (counts) of the number of gray whales in the lagoon to monitor habitat use, and the on-going collection of photographic identification information (Photo-ID) of individual whales, especially females with calves that are indicative of the reproductive health of the population.
Monitoring of the number of gray whales that utilize Laguna San Ignacio and within other wintering gathering areas in Baja California indicate that water temperature can have an effect on the duration and lengths of their migration, and the aggregation areas the whales choose to use each winter. In the winter of 2009 the water temperature in the lagoon was 16-19 degrees °C during February and March, which was 2-3 degrees °C[MG1] warmer than in the previous winter, and this could account for the greater number of whales seen in the lagoon this year. The trends in water temperature within Laguna San Ignacio in 2009 were measured using autonomous recording devices placed on the bottom of the lagoon by the marine Acoustics program (see below). The water temperature reached a minimum of 15-16 degrees °C in mid February, and increased to a high between 19-20 degrees °C the first week in March.
Weekly census counts of the number of whales in the lagoon began on January 19th 2009 and continued until the first week in April 2009. The greatest number of adult whales counted was 193 adults including 30 mother-calf pairs counted on 24 February 2009 (Fig. 1). As the season progressed, larger numbers of mother-calf pairs were seen in the lagoon in March (Fig 2). Most gray whale calves are born by mid-February, so this increase late in the season suggests that females with older calves born elsewhere were entering Laguna San Ignacio. This late season increasing trend has been seen in the lagoon since 1978-1982 census counts.
This suggests that females with older calve calves were using the lagoon later in the winter before beginning their migration north. Review of the photographic identification data for females with calves visiting the lagoon in recent years will determine if these female-calf pairs have been in Laguna San Ignacio all season, or if they arrived at the lagoon from other areas later in the season.
This year Team member Sergio Martínez (UABCS) re-designed the data-base for all the digital images of gray whales since the year 2006 when digital photography replaced the older film and paper based technology. The new database is patterned after the humpback whale database used to archive, organize, sort and search digital images of humpback whales from Mexico as part of the “SPLASH” Pacific humpback population estimation project. This new database management system will allow Laguna San Ignacio gray whale researchers to update and manage digital images of whales and their associated meta-data, and to produce summary reports and image catalogues as new photographs are obtained. These catalogues will be posted on the LSIESP web-site to facilitate review by gray whale researchers working in other portions of the ENP gray whales’ range, and allow them to compare their photographs and to identify possible matches with whales photographed in Laguna San Ignacio.
As with previous years, the 2009 digital photos are sorted into two groups – mothers with calves and single whales, and then compared within the season to estimate minimum duration of stay of these whales in the lagoon, and also compared with photos from previous seasons to identify re-sightings of known individual whales, especially females that have been seen with and without calves in previous years. The calving intervals for these females are then estimated from the number of years they are seen with and without calves in the lagoon, and within year estimates compared for trends across years.
The gray whale Team is also tracking the number of “skinny” whales that visit the lagoon. “Skinny” whales are those that exhibit some evidence of nutritional stress presumably as the result of insufficient feeding during the summer and/or disease. The photos of whales are assigned numerical scores based on three physical characteristics of nutritional stress. This scoring system was developed by Dave Weller and his colleagues to evaluate the health of Western North Pacific gray whales. These condition criteria are:
- degree of post-cranial depression,
- prominence of dorsal edge of the scapula, and
- degree of concavity of the lateral flanks. In 2007 and 2008 approximately 11-13% of the gray whales photographed in Laguna San Ignacio exhibited some or all of these indicators of nutritional stress.
The 2009 photographs will be similarly analyzed and compared.