EXTANT BATOIDS

Pelagic Stingray Shed Rates & Sampling

Jim Bourdon, Scott Greenwald and Henry Mollet
Illustrated by Jim Bourdon, Copyright © 1997

Study Overview

Several parallel areas of study envolved the pelagic rays at the Monterey Bay Aquarium. Some of these are unrelated to this study, such as feeding, inter and intra-specific behavior, others important but not directly relevant, the development of siphoning techniques for the recovery of teeth and denticles, and others of primary relevance. This page is intended to provide certain comparative data relevant to this study.

Participating rays

Six rays have been working very hard to provide the authors with data for this study -- two males and four females. They have fared well in their captive environment as reflected by their recent growth charts and the authors' inability to obtain a female dentition.

DATE	SEX	QTY	Disc Width	WEIGHT	FILE COUNT	COMMENTS
Dec. 96	Male	2	53, 57 cm.	4.6, 6.9 kg	.	.
.	Female	4	69, 70, 75, 83 cm	13.0-22.7 kg	.	.
Mar. 97	Male	2	55, 59 cm	5.8, 8.2	.	.
.	Female	4	73, 73, 79, 84 cm	16-25 kg	.	.

Method Options

A primary objective of this study is pelagic stingray shed rates -- the regular replacement of functional teeth. The ultimate goal is to determine these rates on a seasonal basis by sex, preferably, by tooth position. To achieve the higher resolutuions of detail requires one of two methods.

Tooth Marking. In this method, various teeth are marked (burr or drill marks left on selected teeth) and the progression of each series can be periodically checked. This approach would require biweekly removal of the rays for study and dental work. It is uncertain what the impact of a years' worth of this repeated handling may have on the rays and if the trauma itself may alter the results.

Collecting and counting shed teeth. The alternate method is to collect and count the teeth shed by the rays. This method presents a number of challanges (collecting, identifying, etc.) but would prove harmless to the rays. It was decide to pursue this second method.

Collecting Shed Teeth

Scott Greenwald devised a filtering mechanism to capture teeth during the siphoning process of the weekly tank cleaning. Preliminary results seemed excellent -- over a hundred teeth were captured during the first three week test. Improvements in the design and fine tuning of the system increased recovery rates significantly.

The early samples provided source material for Jim Bourdon to commence study of the teeth themselves. The teeth were grouped by type as a first step in identifying them as to sex and dental position. To prevent the study from becoming side tracked by details, two parallel studies were initiated.

THE MACRO TRACK

The first would take a broad approach, determining a blended shed rate for the species. This is being done by the weekly collecting and counting of the teeth (and denticles) by Scott and Henry Mollet. The teeth are differentiated only as being high or low-cusped. The results of those efforts is summarized in the first table below. The "Shed Rate" as noted in the table is the number of series (one tooth from each file) shed per week. At the time of this wiritng, the total number of files in the studied rays is not known. For interim purposes, the basis employed will be 35 files per dental band. This number is the median tooth count provided by Nishida & Nakaya (1990) for six males and two females.

THE MICRO TRACK

The secondary course (micro approach) is a monthly effort based on the mid-month sample. It will attempt to group the teeth into the twenty-or-so tooth-types which have been assigned. As greater knowledge is achieved, these counts should be convertible into sex and tooth position.

WEEKLY TOOTH COUNTS

DATE	High	Low	Bicusp	Patho	Total	Shed Rate	Denticles	Thorns	COMMENTS
	cusp	cusp
Jan 17	52	78	7	1	138	.33 series	22	.	.
Jan 24	?	?	?	?	?	?	?	?	may be in 2-14
Jan 31	n/a	n/a	n/a	n/a	n/a	n/a	n/a	n/a	included in 2-14
Feb 7	n/a	n/a	n/a	n/a	n/a	n/a	n/a	n/a	included in 2-14
Feb 14	230	208	33	11	482	.38 series	30	1	3 or 4 week sample
Feb 21	84	104	22	2	212	.50 series	54	.	.
Feb 28	50	54	11	2	117	.28 series	15	5	.
Mar 7	67	75	6	4	152	.36 series	23	15	.
Mar 14	60	63	13	4	140	.33 series	28	5	.
Mar 21	51	81	13	5	150	.36 series	54	.	.
Mar 28	43	57	9	1	110	.26 series	18	.	.
Apr 4	57	72	17	0	146	.35 series	27	.	.
Apr 11	70	73	12	4	159	.38 series	22	.	.
Apr 18	61	68	9	1	139	.33 series	39	.	2nd syphon
Apr 25	75	74	17	3	169	.40 series	60	.	2nd syphon
May 2	49	73	10	5	137	.33 series	31	.	2nd syphon
May 9	65	67	7	1	140	.33 series	65	.	2nd syphon
May 17	62	97	5	1	165	.34 series	45	.	8 day sample, rate adjstd
May 23	51	51	12	1	115	.32 series	28	.	6 day sample, rate adjstd
May30	67	75	15	4	161	.38 series	34	.	.

MONTHLY TOOTH STUDY

The following table reflects the results of a particular sample and the month it was taken. Noted parenthetically is the number of bicusped teeth within a particular group count. Pathological teeth have not been included in the total, but their number is shown at the end of each month.

ANTERIOR

Nr	Mnth	54c	54b	58a	58b	60c	58-d	nyi3	58c	60a	Total	Bicusp
.	Feb	.	.	.	.	.	.	.	.	.	.	.
0314	Mar	12	15(2)	3	3(1)	2	11	3	10(1)	5	64	4
.	Apr	.	.	.	.	.	.	.	.	.	.	.

LATERAL

Nr	Mnth	54d	54e	nyi6	55b	nyi5	60c	Total	Bicusp
.	Feb	.	.	.	.	.	.	.	.
0314	Mar	10(4)	9(3)	5	2	3	3(1)	32	8
.	Apr	.	.	.	.	.	.	.	.

POSTERIOR

Nr	Mnth	54a	nyi7	58e	nyi9	55d	Total	Bicusp	.	Patho
.	Feb	.	.	.	.	.	.	.	.	.
0314	Mar	7	3	6(1)	2	22	40	1	.	4
.	Apr	.	.	.	.	.	.	.	.	.

DENTICLES

Nr	Mnth	D1	D2	D3
.	Feb	.	.	.
0314	Mar	5	19	6
.	Apr	.	.	.

Go to:	Pelagic Stingray Home Page,	Dentition,	Shed Teeth,
	Reference Material	Denticles	Glossary

Page revised July 31, 1997