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The handle http://hdl.handle.net/1887/33217 holds various files of this Leiden University dissertation.
Author: Osinga, Nynke
Title: Comparative biology of common and grey seals along the Dutch coast : stranding, disease, rehabilitation and conservation
Issue Date: 2015-06-09
Appendix
Data for live-stranded common
and grey seals 1
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1
Data for live-stranded common and grey seals
Recent data on live stranding of common seal have been added to the data presented in Chapter 1. The dataset now comprises all live-stranded common seals admitted for rehabilitation during the period from 1971 until June 1st 2013 (n=4,958). In addition, data on grey seal live strandings were analysed by comparable methods to the analysis of common seal live strandings in Chapter 1. The dataset for grey seals comprises all live- stranded seals admitted for rehabilitation during the period from 1971 until November 1st 2013 (n=1,705).
Instead of numbers per calendar year, seals were categorised per so-called seal year.
For the common seal, a new seal year starts with the stranding of the first orphan, which is usually in May. For grey seals, the new seal year starts with the first orphaned grey seal stranded in autumn, which is usually in November or December.
Common seals
Four categories can be distinguished. Orphaned seals comprise the first category (n=1,556, 31.4%, see Figure 1). They were categorized as orphans based on their length, weight and the diagnoses recorded in their rehabilitation files. The second category consists of seals which are weaned but stranded in an emaciated condition with complications (n=408, 8.2%). The third category consist of seals which have been diagnosed with parasitic bronchopneumonia; this category proved to be the largest group (n=2,708, 54.6%). The remaining seals stranded due to a range of different conditions, such as parasitic, bacterial and viral infections, as well as injuries and skin lesions, and other causes (n=286, 5.8%).
This category also includes the sub-adult and adult seals.
Since 2008, there has been a continued increase in live strandings of orphaned seals.
There has however been a steep increase in the number of parasitic pneumonia cases; with 300-500 stranded seals per year since 2009.
Grey seals
Grey seals were divided into the same four categories as used for common seals. The first category concerns orphaned seals (n=684, 40.1%, see Figure 2). They were categorized as orphans if the presence of an umbilical cord and/or a lanugo was recorded in their rehabilitation files. The second category consists of seals which are weaned but stranded in an emaciated condition with complications (n=769, 45.1%). Grey seals were categorised as weaned when they had shed their lanugo. The third category consists of seals diagnosed with parasitic bronchopneumonia (n=108, 6.3%). The remaining seals stranded due to a variety of other causes (n=144, 8.4%).
Generally, the number of stranded grey seals increased over the period investigated, which is in line with the growing number of grey seals in Dutch waters. The number of stranded, orphaned grey seals appears to fluctuate greatly between years (for comparison with common seals, see Figure 1). Another finding is that the number of weaned grey seals that stranded is rather high compared to common seals.
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1
Appendix 1
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800
71-72 72-73 73-74 74-75 75-76 76-77 77-78 78-79 79-80 80-81 81-82 82-83 83-84 84-85 85-86 86-87 87-88 88-89 89-90 90-91 91-92 92-93 93-94 94-95 95-96 96-97 97-98 98-99 99-00 00-01 01-02 02-03 03-04 04-05 05-06 06-07 07-08 08-09 09-10 10-11 11-12 12-13
N
Seal year total
orphan weaned parasitic pneumonia other
0 20 40 60 80 100 120 140 160 180
71-72 72-73 73-74 74-75 75-76 76-77 77-78 78-79 79-80 80-81 81-82 82-83 83-84 84-85 85-86 86-87 87-88 88-89 89-90 90-91 91-92 92-93 93-94 94-95 95-96 96-97 97-98 98-99 99-00 00-01 01-02 02-03 03-04 04-05 05-06 06-07 07-08 08-09 09-10 10-11 11-12 12-13
N
Seal year total
orphan weaned parasitic pneumonia other
Figure 2. Numbers of live-stranded grey seals admitted for rehabilitation, per seal year (1971-2013) Figure 1. Numbers of live-stranded common seals admitted for rehabilitation, per seal year (1971- 2013).
