Vol. 10 (2): November 2007

Response of monk seals to
monitoring activities on the Mersin coast

Ali Cemal Gücü

Levant Nature Conservation Society

In 1995, when the first monk seal survey on the Mersin coast had been concluded, the main aggregation of monk seals was found to be on the pristine coast stretching between Tasucu and Gazipasa. Although there were occasional seal sightings, no resident seals could be spotted in neighbouring sites. Later, in 2003, a seal began frequenting a cave located outside the range of the colony, near to an urbanized area.

To prevent human entry and hence provide a better shelter, the Levant Nature Conservation Society blocked the terrestrial access to this cave in July 2005 [see Monk seal cave closed to land access, TMG 9(1): June 2006]. The cave has since been equipped with camera and infrared sensors to monitor seal presence. At first, a single female was recorded in the cave on an irregular basis. In 2006, the female was accompanied by a young male, apparently yet to attain maturity.

As of July 2007, however, the cave is now being used by 3 different seals among which the female (Ceren) has significantly prolonged her stay in the shelter. Initially, the seal(s) were recorded mainly at night (dusk to dawn). Later, this pattern shifted slightly, with haul-out times spread intermittently throughout the day. As the entry to the cave by humans had been confined to daylight hours before the closure, the changes in the cave use pattern may be a positive sign of protection.

The monitoring systems used until now are composed of an infrared sensor sensitive to heat in motion, which triggers a digital camera with programmable intervals. The digital camera has a resolution of 5.1 megapixels. The camera also incorporates a built-in flash that is sufficient to illuminate a range of 7 meters. This combination is essential to obtain images detailed enough to be used in photo-identification.

Depending on the desired length of use, which may extend up to 2-3 months, the interval between 2 subsequent camera shots is set at between 10 to 30 minutes. That means that every 10 to 30 minutes the camera flashes if a seal is within detection range. The images obtained from the camera demonstrate that the flash is recognized by the seals; there are several cases in which the animals have their head extended or directed toward the camera. Hence, the concern was raised whether the flash disturbs the seals or not (Fig. 1).

Fig. 1. Seal appearing to react to the camera flash.		Fig. 2. A seal appearing to react to the infrared light source.

The Levant Nature Conservation Society therefore began testing the effects of flash use on the seals. Two cameras, one with flash and the other with infrared light source are now being deployed in the cave consecutively each for an average deployment time of one week. The system is then replaced with the other in order to discount possible behavioural change by the seal due to time/season. Until now, 192 events have been recorded by the cameras. The first and preliminary results show that the average haul-out duration of a seal exposed to a flash is longer than those recorded by infrared light source. Evaluation of the results of the two systems did not show a statistically significant difference (F test: p>0.05).

The number of times that a seal was exposed to the flash during a haul-out varied between 1 and 27. This number is slightly lower than compared to infrared shots. The average shots of the two systems are almost identical (F test: p>0.05).

Table: Statistical results.

All additional features of the camera, such as red-eye pre-flashing, audible click etc. are disabled in order to minimise as far as possible any unnecessary disturbance.

Some images obtained in infrared mode suggest that seals may react briefly to the triggering of the infrared bulbs that momentarily turn red when activated (Fig. 2). However, the light is sufficiently brief and unobtrusive that the animals quickly resume their resting and haul-out behaviour.

Fig. 3. Seal captured in infrared mode, where little image detail is available.		Fig. 4. A hauled-out seal captured by the camera operating in flash mode. Colouration and marking is clearly visible compared to images obtained in infrared mode.

Collecting data of this kind is inherently difficult because of the rarity of the species. However, the data at hand, although scarce, provides evidence that the use of built-in flashes with 10-minute intervals does not inflict disturbance upon the seals in the cave. The use of colour images in seal photo-identification has great advantages over infrared images, in which the details, such as scars and discolorations, are inevitably faded out (Fig. 3 & 4).

Fig. 5 and 6. On 30 October, shortly before this article went to press, the infrared monitoring system recorded a mother with newborn pup in the cave.

The author expresses his thanks to Giulia Mo of ICRAM for commenting upon and reviewing this article.

Copyright © 2007 Ali Cemal Gücü, The Monachus Guardian. All Rights Reserved