Baleen species（在这里指的是须鲸类） 【studied at close quarters underwa

Baleen species（在这里指的是须鲸类） 【studied at close quarters underwater】 have obviously tracked objects with vision underwater.这句的中文翻译是：通过研究须鲸发现,其可以在封闭的水下追踪物体.这句话中Baleen species在从句中做主语,并且还在从句中表被动,为什么不写be动词,也就是写成：Baleen species that were studied at close quarters underwater have obviously tracked objects with vision underwater.老师没说过在被动句中,be可以省略的情况啊?网上查了一下,要是不写be的话 好像还犯了语法错误了,那么这难道是英国人口语化的结果?而且that作宾语才能省略,做主语好像不能吧?