Weddell seal survey days are long ones for the field team. The team will cover the entire Erebus Bay study area in one 24 hour period to count, identify, and record every seal encountered during that single sweep. To accomplish this, the team will travel by snowmobile to the all different Erebus Bay pupping colonies, and move quickly through those colonies to record every seal they come across.
This survey information is recorded in both the small field books the researchers carry and the hardy handheld field computers they use on the ice. Back in camp after the survey, data entered into the field books will be compared with the data entered into the field computers to ensure accuracy of the count. Lead scientist Jay Rotella notes, "For each seal observation, we record the date, location, seal tag numbers, sex, age class. For females with pups, we also record that they are a pair. For a subsample, we also collect a very small tissue sample for genetics work and record that. If we weigh the seal or outfit it with a swim tag, we also record that information."
Since Weddell seals spend a good amount of time in the water, they may not be visible to the team when it moves through an area on a particular occasion. To address this, 6 to 8 full surveys will be conducted over the pupping season. This makes it more likely that the researchers will encounter every seal in the study area at some point during the survey period, and so achieve an accurate count of the entire Weddell seal population in the study area for the current season.
Co-PI Don Siniff writes in an unpublished manuscript on the history of the Weddell population project that, "In 1973 the decision was made to tag all the pups born into the McMurdo population as well as a significant number of adult females."
"When the effort to tag all the pups born into the McMurdo population was initiated an effort to walk through the pupping colonies and record all the individuals present, along with the tag numbers, was begun. These 'census' efforts were generally repeated at least seven times each pupping season and the census tallies became the central part of the growing database."
"Initially, data from these census undertakings were recorded in a standard field notebook," Siniff explains, and that practice continues to this day. "In the mid 1980s, small handheld computers became available. This started a process of developing a data entry system that could be used to record tag numbers and the other data as we moved through the pupping colonies."
"Ward Testa was instrumental in this development at this time, and wrote the first data entry program which contained routines that checked each entry as it was entered to make sure the new data were consistent with what was already in the data base. This data checking routine proved extremely valuable in limiting the number of mistakes entered into the data base."
More work on improving the field computers was done by Michael Cameron, who worked as a PhD student with Don Siniff on the Weddell project for a number of seasons. Siniff notes, "In the late 1990s Michael Cameron contributed significant upgrades to what Ward Testa had developed, and we purchased new field computers as they came on the market. This was essential as the database was continually increasing in size and the data checking programs needed additional computer storage space and increased speed."
"In 2002 the project moved to Montana State University with Jay Rotella and Bob Garrott as lead principal investigators. The data entry program was rewritten by the Montana State University program in order to take advantage of the upgrades in handheld computers and bring the data entry software up to date. Since its arrival at MSU, the database has been subjected to analyses taking advantage of the fact that the McMurdo population database currently consists of over 80 percent known-age individuals."
This season, the team is using a new field computer called the Trimble Ranger 3, shown in the photo below, which includes GPS capability.
Notes Siniff, "The database now consists of perhaps the most complete record on marked individuals that have been seen repeatedly over their lifetimes. These data can now be subjected to advanced statistical analyses, using the latest programs and models that make up a major area of study focusing on multiple mark-recapture data. A number of population statistics can be accurately estimated from such analyses, including the investigation of ecosystem measures whose influence on the dynamics of the Weddell population can now be explored in detail."
Learn more about the Weddell seal population study project at WeddellSealScience.com.